Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Rupture between Antiochus and the Romans
Antiochus took his resolution. A rupture with Rome, in spite of endeavours to postpone it by the diplomatic palliative of embassies, could no longer be avoided. As early as the spring of 561 Flamininus, who continued to have the decisive voice in the senate as to eastern affairs, had expressed the Roman ultimatum to the envoys of the king, Menippus and Hegesianax; viz. that he should either evacuate Europe and dispose of Asia at his pleasure, or retain Thrace and submit to the Roman protectorate over Smyrna, Lampsacus, and Alexandria Troas.
These demands had been again discussed at Ephesus, the chief place of arms and fixed quarters of the king in Asia Minor, in the spring of 562, between Antiochus and the envoys of the senate, Publius Sulpicius and Publius Villius; and they had separated with the conviction on both sides thata peaceful settlement was no longer possible. Thenceforth war was resolved on in Rome.
In that very summer of 562 a Roman fleet of 30 sail, with 3000 soldiers on board, under Aulus Atilius Serranus, appeared off Gythium, where their arrival accelerated the conclusion of the treaty between the Achaeans and Spartans; the eastern coasts of Sicily and Italy were strongly garrisoned, so as to be secure against any attempts at a landing; a land army was expected in Greece in the autumn.
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Reference address : https://www.ellopos.net/elpenor/rome/3-09-war-antiochus-asia.asp?pg=14