|Signet ring bearing the image of Scipio|
In 190 Scipio was sent as legate to his brother Lucius, who was consul in command of the Roman army in the war against Antiochus III of Syria (supported by Hannibal). In fact, Scipio had engineered the election of both Lucius and Gaius Laelius in order to ensure for himself the effective command.
The first project for the Romans was to secure naval supremacy. This they did, with the considerable help of the Rhodians and Pergamenians, and some aid from Carthage. The Syrian fleets were defeated in three battles. In one of these sea battles, at Side in 190BC, fought against Eudamus of Rhodes, Hannibal had fought - and lost - his first and last naval engagement.
Antiochus now blundered into withdrawing his garrisons from Lysimachia and gave up the defence of the Hellespont. Scipio, meanwhile, had marched through Greece with an army composed of Glabrio's old army plus two legions from Italy. In addition, 5,000 veterans had volunteered to serve under their beloved leader.
If Antiochus had chosen to contest the passage of the Hellespont, he, no doubt, could have forced Scipio into winter quarters in a very disadvantageous position. Having crossed his army, Scipio remained behind due to his religious duties as high priest. Antiochus spent his time (as before Thermopoly) in sensual pleasure at his court. When it was too late, he sent envoys to ask for peace. Scipio replied that he might have accepted the king's terms while still in Europe, but now that the Romans were in Asia, Antiochus would have to surrender all Asia Minor.
The King returned Scipio's son, whom he had captured, and tried to bribe the general, but to no avail. Even now the King might have had some success by refusing battle and withdrawing into the interior. Instead he hastened to met the trained Roman legions with his ill-organized mass of Asiatic levies. Antiochus' force was about 80,000 strong, of whom 12,000 were cavalry. The Roman army including Greek and Macedonian allies was less than half that figure. Scipio fell sick and returned to the sea coast. The army was now commanded by Gnaeus Domitius Ahenobarbus.
Antiochus had difficulty squeezing his forces into the restricted space available in the Hermus River valley, near Magnesia in Asia Minor. Hannibal was present, although probably under a cloud, following the disgrace of his defeat by Eudamus, and is not reported as playing any major role in the battle.
Here, in 190BC, Antiochus suffered a major defeat. And Hannibal's safe haven was under threat.