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
War against Nabis of Sparta
The regulation of the affairs of the Greek states, as respected both their mutual relations and their internal condition, was attended with difficulty. The most urgent matter was the war which had been carried on between the Spartans and Achaeans since 550, in which the duty of mediating necessarily fell to the Romans. But after various attempts to induce Nabis to yield, and particularly to give up the city of Argos belonging to the Achaean league, which Philip had surrendered to him, no course at last was left to Flamininus but to have war declared against the obstinate petty robber-chieftain, who reckoned on the well-known grudge of the Aetolians against the Romans and on the advance of Antiochus into Europe, and pertinaciously refused to restore Argos.
War was declared, accordingly, by all the Greeks at a great diet in Corinth, and Flamininus advanced into the Peloponnesus accompanied by the fleet and the Romano-allied army, which included a contingent sent by Philip and a division of Lacedaemonian emigrants under Agesipolis, the legitimate king of Sparta (559). In order to crush his antagonist immediately by an overwhelming superiority of force, no less than 50,000 men were brought into the field, and, the other towns being disregarded, the capital itself was at once invested; but the desired result was not attained. Nabis had sent into the field a considerable army amounting to 15,000 men, of whom 5000 were mercenaries, and he had confirmed his rule afresh by a complete reign of terror--by the execution -en masse- of the officers and inhabitants of the country whom he suspected.
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Reference address : https://www.ellopos.net/elpenor/rome/3-08-second-macedonian-war.asp?pg=64