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
But these noble arrangements were only the first steps towards a complete remodelling of Rome. Projects were already formed for a new senate-house, for a new magnificent bazaar, for a theatre to rival that of Pompeius, for a public Latin and Greek library after the model of that recently destroyed at Alexandria-- the first institution of the sort in Rome--lastly for a temple of Mars, which was to surpass all that had hitherto existed in riches and glory. Still more brilliant was the idea, first, of constructing a canal through the Pomptine marshes and drawing off their waters to Tarracina, and secondly, of altering the lower course of the Tiber and of leading it from the present Ponte Molle, not through between the Campus Vaticanus and the Campus Martius, but rather round the Campus Vaticanus and the Janiculum to Ostia, where the miserable roadstead was to give place to an adequate artificial harbour.
By this gigantic plan on the one hand the most dangerous enemy of the capital, the malaria of the neighbourhood would be banished; on the other hand the extremely limited facilities for building in the capital would be at once enlarged by substituting the Campus Vaticanus thereby transferred to the left bank of the Tiber for the Campus Martius, and allowing the latter spacious field to be applied for public and private edifices; while the capital would at the same time obtain a safe seaport, the want of which was so painfully felt. It seemed as if the Imperator would remove mountains and rivers, and venture to contend with nature herself.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=95