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
Abolition of the Dictatorship
Under the former head the most important innovation was the practical abolition of the dictatorship. The crisis occasioned by Quintus Fabius and his popular opponents in 537(61) gave the death-blow to this all-along unpopular institution.
61. Cf. III. V. Fabius and Minucius
Although the government once afterwards, in 538, under the immediate impression produced by the battle of Cannae, nominated a dictator invested with active command, it could not again venture to do so in more peaceful times. On several occasions subsequently (the last in 552), sometimes after a previous indication by the burgesses of the person to be nominated, a dictator was appointed for urban business; but the office, without being formally abolished, fell practically into desuetude. Through its abeyance the Roman constitutional system, so artificially constructed, lost a corrective which was very desirable with reference to its peculiar feature of collegiate magistrates;(62) and the government, which was vested with the sole power of creating a dictatorship or in other words of suspending the consuls, and ordinarily designated also the person who was to be nominated as dictator, lost one of its most important instruments.
62. Cf. II. I. The Dictator
Its place was but very imperfectly supplied by the power--which the senate thenceforth claimed--of conferring in extraordinary emergencies, particularly on the sudden outbreak of revolt or war, a quasi- dictatorial power on the supreme magistrates for the time being, by instructing them "to take measures for the safety of the commonwealth at their discretion," and thus creating a state of things similar to the modern martial law.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=77