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
A battle took place, in which nearly 1000 Spartans fell, and Sparta might have been taken if Damocritus had not been equally incapable as an officer and as a statesman. He was superseded, and his successor Diaeus, the instigator of all this mischief, zealously continued the war, while at the same time he gave to the dreaded commandant of Macedonia assurances of the full loyalty of the Achaean league. Thereupon the long-expected Roman commission made its appearance, with Aurelius Orestes at its head; hostilities were now suspended, and the Achaean diet assembled at Corinth to receive its communications. They were of an unexpected and far from agreeable character. The Romans had resolved to cancel the unnatural and forced(20) inclusion of Sparta among the Achaean states, and generally to act with vigour against the Achaeans.
20. Cf. III. IX. The Achaeans
Some years before (591) these had been obliged to release from their league the Aetolian town of Pleuron;(21) now they were directed to renounce all the acquisitions which they had made since the second Macedonian war--viz. Corinth, Orchomenus, Argos, Sparta in the Peloponnesus, and Heraclea near to Oeta--and to reduce their league to the condition in which it stood at the end of the Hannibalic war.
21. Cf. III. IX. The Achaeans
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Reference address : https://www.ellopos.net/elpenor/rome/4-01-gracchi.asp?pg=77