The career of Great King Antiochos the Great of the Seleukid Empire is one filled with both successes and failures.  After the reversal at Raphia, Antiochos had continuously campaigned and done so victoriously from Mikra Asia to India and back again.  And with the victory at Panion, he had solidified himself and his realm at the preeminent position in the Mediterranean and Asian world.  However, it would be the events afterward that would slowly build up to a conflict with the Roman Republic and undo the labors of Antiochos.
The campaign of Antiochos III in Koile-Syria and Mikra Asia ran concurrently with Rome’s involvement in Greece.  As Rome prepared itself for war with Philippos V of Makedonia in 200 BC, she sent envoys to the three Diadochoi states and became very concerned with the developments in Syria.  It was very clear that Antiochos was winning his war for control of Koile-Syria and Phoinike and by the time his respective Roman envoy had left his victory at Panion would have already happened.  Essentially, the envoy was seeking to ensure that Antiochos would not interfere with the events in Greece and Makedonia.  This was, of course, not an issue for Antiochos as he was still involved with the fighting in Syria, and Philippos had shown himself to be more than willing to cause trouble in Mikra Asia, which needed many more years of stability if it were to be integrated again within the Seleukid Empire with confidence.
After the fall of Gaza in 198 BC, Antiochos moved to retake territorial possessions that his family had lost, retaken, and lost again throughout the Syrian wars in Mikra Asia. He had organized an extensive land and sea operation systematically removing Ptolemaic garrisons; however, his actions did not go unnoticed by other regional powers.  Two in particular would have consequences for Antiochos immediately and less than a decade later.
The first of these was Attalos I of Pergamon, who claimed that Antiochos was invading his territories.  This was quite a ludicrous claim since the reality of the situation as that Antiochos and Attalos had been allied since Antiochos’ campaign against Achaios.  Attlos’ claims should not be a seen as surprising since he had been quite adept at getting Rome to fight his battles for him.  And although Rome did nothing to aid him, he used this as an excuse to pull out of the 2nd Makedonian War.  Rome did, however, send an envoy to Antiochos to again ensure that he would not interfere with the events in Greece, to which  Antiochos responded by sending his own diplomat to Rome earning him the vague status of amicitia.
The second power was Rhodos, who claimed to be acting in Rome’s interest by demanding that Antiochos cease his military actions.  Of course, this claim had no backing as the very embassy Antiochos sent in response to the Rhodian demands had just returned from Rome herself.  Rather than risk coming into conflict with Rhodos, however, Antiochos proposed an alliance and a division in the spoils of the Ptolemaic holdings in Mikra Asia as well as allowing the Rhodians to retake holdings they had lost to Philippos’ expeditions in 201.  In fact, Antiochos participated in the fighting to retake the city of Stratonikeia from a Makedonian garrison by the Rhodians.  And although Antiochos could claim this city as it was founded by one of his ancestors, by allowing the Rhodians some territorial gains it actually hemmed them into a small corner of Mikra Asia and thereby removing them as a threat to the regions stability.
After passing the areas assigned to Rhodos as part of their pact, Antiochos continued his expedition and by the time of the fighting at Kynoskephalai he was firmly established in Ionia and based at Ephesos.  A number of the cities now under Antiochos had suffered badly during Philippos’ campaigns only a few years before.  In the case of at least Iasos, the city received significant aid by Queen Laodike, wife of Antiochos.  Unfortunately, the death of Attalos of Pergamon threatened the stability of the situation.
Pergamon had always been a troublesome issue for the Seleukids.  Recent events though managed to work in Antiochos’ favor and he was able to craft an alliance against his uncle Achaios with Attalos.  Standard Hellenistic practice operated with a clear termination clause: the death of one of the signers.  With the Pergamene king dead, the heir Eumenes II was under no obligation to align himself with Antiochos.  Furthermore, continuing the good relations with Rome that his father had begun, he likely found an alliance with the far off republic more attractive than the massive power next door that was Antiochos.  Although Eumenes did not declare against Antiochos immediately, he did reject overtures for a continuance of the alliance.  The complicated political situation in Mikra Asia became more complicated.
For now, Antiochos left Eumenes alone.  Deciding not to pressure the young king he moved north and continued to gain control over the Greek cities that occupied the north-western portion of the massive peninsula.  His policies for these cities were essentially internal autonomy, but submission for external relations as they affected the empire.  Of these cities two would be problematic for the king: Smyrna and Lampsakos.  Both were formerly under Seleukid domain, both broke free during the troubles of the mid-3rd century, both were at one time allied to Attalos I of Pergamon, and now both surprisingly appealed to Rome in the face of Antiochos’ demands.
Eventually, both found themselves isolated by Antiochos and even then Lampsakos had a hard time finding someone willing to go to Rome, which suggests that the populace of the city found Antiochos demands as amenable.  Other cities had not put up resistance and when there were, only token shows of force were presented to the Greek cities.  What was important was that the Roman consul in Greece and victor of Kynoskephalai T. Quinctius Flaminius became acutely aware of the Seleukid king’s activities, which bothered both him and the Roman Senate – especially the big question of what Antiochos was going to do now.
Of all the cities that Antiochos brought into his hegemony, Abydos was one of the most important.  Despite the citizens committing mass suicide rather than fall to the depredations of Philippos V’s campaigns, the city was located at the major crossing point across the Hellespont.  Although a subtle hint as to his plans, Antiochos’ intentions were well known when he crossed over to Chersonese and restored the city of Lysimacheia in 196 BC.
The people of the Chersonese welcomed this as Lysimacheia was a wall of protection from marauding Thraikians until its destruction.  It was also a major political statement that shouted to the Greek world that the Greek cities would be safe under Antiochos’ rule compared to the rules of others or the isolation of independence.  This was in conflict with Flaminius’ announcement in the same year that the Greek cities shall be “free”.  While the term is incredibly relative, as far as Rome was concerned the Greek cities would be freer under her authority than under Antiochos’.  This also meant that the peace Flaminius was carefully crafting could fall apart before it began.  A delegation was sent to Lysimacheia.
The Roman delegates arrived at the restored Lysimacheia while Antiochos was busy in Thraike.  Twice Thraike was a part of the Seleukid Empire so Antiochos was hardly going to let the campaign season go to waste.  However, not only did this worry the Roman delegation since Antiochos was now closer to Greece than ever, but it also worried Philippos since the treaty with Rome drastically reduced his power while Antiochos was essentially next door.  Rome wanted a guarantee that Antiochos would not interfere with Greece and as soon as the king returned from his campaign the conference began.
As before, Antiochos allayed Roman fears.  His goal was only to restore the Seleukid rule to lands which were formerly under his ancestors’ control.  This argument was bolstered by his surprising statements that peace negotiations between him and the Ptolemaioi were close to being concluded, that Lysimacheia was restored as a kingdom for his son Seleukos, and that he wanted an alliance of equals with Rome.  Both parties left the conference having reached an agreement: Smyrna and Lamsakos would be under Roman protection along with Rhodian mediation and Antiochos could continue his operations in Thraike without Roman objection.  For now the two major powers maintained their peace and seemed to have left on friendly terms.
The winter of 196 through the spring of 195 was a busy time for both parties.  Flaminius had his hands full keeping the difficult parties of Greece together and fighting against Nabis of Sparta.  Antiochos was to attend the wedding of his daughter Kleopatra to Ptolemaios V to ratify the peace treaty for the 5th Syrian War, which occurred at Raphia of all places.  He also approached Eumenes for a marriage arrangement (though Eumenes declined), sent envoys to Rome to raise again the proposal for an alliance, and then spent the summer campaigning in Thraike.
When the envoys reached Rome, their proposal was made directly to the Senate.  The responses ranged from not favorable to quite aggressive.  The events of the 2nd Punic War had seriously damaged the Roman people’s collective psyche.  Many senators feared that an alliance with Antiochos could leave them open to attack, and this xenophobia was not helped by the fact that the Seleukid king had welcomed an exiled Hannibal Barca into his court.  Of course, such an attack would be ridiculous, but that did not stop people such as Scipio Africanus from making much noise about the subject and demanding the withdrawal of Antiochos from Thraike, and if not to allow the freedom of the Greek cities of Mikra Asia (a contradiction of the events at Lysimacheia).  For the meantime, it would seem that uncomfortable neutrality would exist between the two powers as Antiochos would not agree to such extreme terms.  Even the philhellene Flaminius was pressured to change his stance from at least considering the alliance to outright rejection.
By the summer of 193 BC we find Antiochos campaigning in Pisidia.  The relative ease and time that it took Antiochos to subjugate Thraike should be appreciated compared to the difficulty Caesar later had with Gaul or Traianus with his Dacian campaigns.  Although Seleukid control may not have been fully guaranteed, that Antiochos was able to change his theater of operation is certainly indicative of at least some measure of success.  Rome was also successful in Greece.  Roman troops had been gone almost a year now and the system set in place by Flaminius had held since then – the defeat of Nabis hemming in Sparta and used to balance the political situation in the Peloponnesos.  This success was not to last.
On their return trip, the Seleukid envoys stopped in Greece to gain a better knowledge of the situation.  It was a natural crossing point from Rome to Ephesos and also a way for Antiochos to leave offerings at Delphi, the main temple to Apollon and progenitor of the Seleukid family.  The most important stop, however, was in Aitolia.
It was the Aitolian League that was most displeased with the situation in Greece as left by the Romans.  They expected to wield more power and control more territory due to their alliance with Rome in the 2nd Makedonian War, but the results left them feeling cheated.  Nabis of Sparta was also among those unhappy with Rome’s involvement and several others as well.  Aitolia then, not willing to look to Rome for a solution, sent out several high profile persons creating a network of those that could be considered definitively anti-Roman.  Interestingly, Philippos V did reject the offers of the Aitolian diplomat; seeing that there was more to gain by overt and clear loyalty to Rome than allying himself with the Aitolian League.
The Seleukid envoys brought all this information to Antiochos as well as notification that Rome had herself sent envoys to negotiate with him.  Of the three, it seems one may have stayed in Greece, the second stayed in Pergamon to continue negotiations with Eumenes (which thereby cemented the relationship between Rome and Eumenes and the latter’s rejection of Antiochos), and the third met Antiochos himself.  The meeting was brief due to the death of Antiochos’ son Antiochos, who was also the junior king.  As a result the negotiations were moved to Ephesos with the Seleukid king represented by a First Friend Minnio while he was in Syria attending to the funeral arrangements.
The details of what actually happened are murky.  It is possible that all that happened was reassertion of the stances of the primary parties.  More importantly for the Romans, upon their return the envoys stated that Antiochos had made neither preparations nor plans for an invasion of Italy or Greece.  Although it seemed simple histrionics (and it was), the current mental condition of the Senate and Rome combined with the presence of Hannibal Barca at Ephesos as a guest of the Seleukid king left the Italian power wary of any perceived threat.  In truth, it was evident that Antiochos was busier solidifying his realm than worrying about expansion: evidenced by his current campaign in Pisidia and the establishment of garrisons in Thraike and Palestine (although, that did not mean that he was not paying attention to events in Greece).  The Roman envoys also brought back news of the deteriorating situation in Greece.
Very quickly it seemed that every party in Greece was becoming dissatisfied with the arrangement Rome left after the 2nd Makedonian War.  It was no longer just Aitolia and the recently defeated Nabis of Sparta, but the Achaian League as well.  War seemed the most obvious choice – so obvious, in fact, that Achaia declared war on Nabis – and the possibilities that conflict could bring were too tempting.  Aitolia, however, never once to mince and not to be outdone, called on Antiochos to arbitrate between the league and Rome as well as “liberate Greece” (both slights against Rome) while at the same time assaulting Demetrias.
Coup d’états, assaults, declarations of war… the Roman effort to liberate Greece and Flaminius’ political architecture collapsed. 
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The losses for both sides are unknown, but were not minimal.  Obviously the grand Seleukid army came out worse.  The losses for the Romans would be most severe in their legions that came under the assault of the cavalry commanded by the Great King himself and the argyraspides.  For the Seleukids it would be most felt in the left wing and core of the army represented by the phalanx.  However, it certainly was not as drastic as at times claimed.  The light infantry would have easily gotten away and a fair amount of cavalry could escape the chariot debacle.  The phalangites would have found their own escape in the confusion of the elephants, which also would have frightened the Roman infantry.  More fighting at the Seleukid camp (an ideal concentration of material for the Romans to loot) would increase losses, but even then most of the Seleukid army would have gotten away and survivors would gradually trickle into fortifications.  Soon after the battle we see Seleukos in the city Apamea-Kelainai east of Magnesia with a significant military force.
After the battle Antiochos made his way to Sardis with several thousand survivors, made preparations for garrisoning the city, and left to join his son Seleukos in Apamea.
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Epilogue:
The events after Magnesia marked what the zenith of Seleukid power and prestige.  The permanent loss of Mikra Asia was a blow to the pride of the empire and the king.  Another result of the battle was the renewed independence of Parthia and Baktria.  In an attempt to once again bring these powers into the Seleukid fold, Antiochos began another anabasis, but died during the looting of a temple in 187 BC in order to procure funds and deny resources to dissident elements in the empire.  It is here that the situation truly begins to deteriorate.  There were, however, two periods of resurgent Seleukid strength.
The first was when Antiochos IV Epiphanes assumed the throne.  Charismatic and competent, he had a string of military victories.  Unfortunately, his successes against the Ptolemaioi were noticed and Rome intervened diplomatically to prevent the Egyptian dynasty’s complete destruction.  Not to be stymied by this and seeing Parthia again threatening the Eastern provinces, Antiochos set off on his own anabasis, which was initially successful – in fact, very much so including the seizing of Armenia.  Lamentably, during this campaign he may have suffered an epileptic fit causing a fall from his chariot and mortally wounding him.  He soon died thereafter.
The second resurgence was when Antiochos VII Sidetes, charismatic and competent as well, managed to stabilize the situation in Syria and mount his own campaign against the Parthians.  Also successful, he continued to push back the Parthians past Media.  His downfall was his decision to winter in the newly conquered territory rather than farther from disputed lands.  After splitting his massive army into smaller contingents in order to stay amongst the many towns, villages, and cities of the region, he was ambushed outside of Ekbatana by the Parthians.  The loss of the king and his massive army was the final blow to the empire – now only a kingdom in Syria rather than an empire of Asia.
Before Antiochos VII, Syria was the scene of constant fighting between branches of the Seleukid house: after, the situation had become much worse.  As time continued the power of the kings further shrank and their rule would often extend no further than around individual cities as partisans continued to wield more power in Syria.  The situation was so unstable that Pompeius Magnus decided that the best course of action was to annex the land into the Roman Republic.  In the end, the infighting of the House of Seleukos was what got the better of the empire by draining of resources and distracting them from greater problems.

Playing the Battle:
As the player you have the option of playing as either Basileus Megas Antiochos III Megas or Consul L. Cornelius Scipio.  The forces of both sides are approximately equal with the Seleukids having an advantage in cavalry and the Romans having a heavy infantry advantage.  Of course, although it is available as a single player battle that does not mean that two cannot have just as much fun.  The multiplayer option has been enabled, which should provide a more challenging experience for the average EB player.

NOTE: 
Many of you who play EB have by now become familiar with many of the big events in the history of the Mediterranean basin.  No doubt that of that many, many have read Livy or other historians both ancient and modern and find themselves focusing on Rome and its achievements.  I am quite certain that among you there is a measure of puzzlement at the sheer size of the Roman force as Livy describes their number at being only 33,000.  I assure you that this is not an error on my part.
Livy as an historian had a specific goal in mind with his writings: to reawaken a sense a virtue in the Roman people, which was perceived to be lost, by writing about the exploits of Rome’s heroes and citizens.  As a result, strictly recounting history is a secondary goal for Livy (although this does not make his writings useless to us) and we see this in his skewing of numbers for the events of Magnesia.  After all, what is more impressive: winning a battle with 50,000+ troops or with 33,000?
So, where did the numbers for the Roman army under L. Cornelius Scipio come from?
The numbers are directly from Livy himself.  Throughout the several hundred lines devoted to recounting the war between Antiochos and Rome Livy continuously mentions specific numbers of troops raised from both Rome and her allies.  It was only recently that those numbers were put together after careful scrutiny by historian John D. Grainger.  Hence the value of 50,000+ for the Roman forces.

FURTHER NOTE:
 Of the reasons cited for Antiochos’ loss at Magnesia one of them is the disposition of his army.  At this point the Seleukid king had over three decades worth of military experience and it would be remiss of us to simply dismiss him as a fool or poor general as he would not have chosen such an arrangement without careful and thorough consideration.  As such, it is necessary to discuss what Antiochos may have intended by his disposition and whether it could have worked at all.
A quick look at the disposition once the battle is started itself gives a fairly accurate representation of the Seleukid army within the limits of the RTW engine.  There are, however, two exceptions.  The first of these is the lack of the “Tarentine” camel archers, which were dropped for the reasons of too many units, too few men per this particular unit (at a ratio of 50:1 there would only be ten men in the unit), and because EB lacks a camel unit.  The second and more important exception is the arrangement of the phalanx and elephants.  
At the battle, Antiochos used what is sometimes known as an “articulating phalanx”, wherein divisions of the phalanx are interspersed with other units to allow more flexibility on different types of terrain and in response to certain types of opponents.  Though first pioneered by Pyrrhos of Epeiros, in this specific example we see elephants grouped in pairs with their attendant guards.  This could be for a few reasons as it would keep the elephants close enough to the front to unnerve the Roman infantry while also leaving them protected.  Another reason could be that if the phalanx was pressed hard enough, then the elephant guards could clear the way allowing the elephants themselves to charge forward into the Roman infantry similar as it happened at Panion.  As it stands, because of unit spacing and limitations in numbers the elephants and their guard were simply placed behind the phalanx. 
So, with these two considerations, what was Antiochos planning considering that he does not even have his phalangites together in one block and what of the chariots?
It seems that Antiochos’ plan was thus:
- Antiochos himself would lead a cavalry charge to split the Roman forces and chase off the routers
- the chariots would severely disrupt the Roman horse allowing them to be brushed aside by the cavalry led by Seleukos
- the phalanx would advance and pin the Roman infantry leaving them open to be either intimidated into surrender or removed piecemeal by the cavalry led by Seleukos
Historically, this of course did not happen.  The chariots went berserk under the fire of the Roman missiles and in their uncontrolled state turned on their comrades (ironically showing us just how effective chariots could be on cavalry) and allowing the Roman cavalry to chase off the entire wing.  The Roman infantry then seized their opportunity and surrounded the phalanx until they broke under the pressure and rampaging elephants.
Had Antiochos been able to more quickly remove the routing legion (for it could certainly rally) he may have been able to return and save the day.  Unfortunately, when leading 4,000 cavalry in the midst of a routing legion it is difficult to gain control of your men and suddenly redirect them – especially if you are unaware of the fate of the other cavalry charge.  As it stands, the blame can be laid on Antiochos’ use of the chariots as expedients in dealing with the Roman cavalry since they were superfluous: the kataphraktoi, hetairoi, and Galatians would have had no trouble dealing with the meager Roman horse. 
Had the chariot attack worked instead of faltering, or had they not even been used, it is safe to say that Antiochos would have carried the day.  The Roman cavalry would have been swept away by the Seleukid horse and the Roman infantry would not have been able to respond to so much cavalry.  Even the triarii with their spears would have found themselves leveled attempting to establish a rear defense before the onslaught of the xyston-equipped kataphraktoi and hetairoi.
