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
About Rome itself new projects were not required; but the Mulvian bridge (Ponte Molle), by which the Flaminian road crossed the Tiber not far from Rome, was in 645 reconstructed of stone. Lastly in Northern Italy, which hitherto had possessed no other artificial road than the Flaminio-Aemilian terminating at Placentia, the great Postumian road was constructed in 606, which led from Genua by way of Dertona, where probably a colony was founded at the same time, and onward by way of Placentia, where it joined the Flaminio-Aemilian road, and of Cremona and Verona to Aquileia, and thus connected the Tyrrhenian and Adriatic seas; to which was added the communication established in 645 by Marcus Aemilius Scaurus between Luna and Genua, which connected the Postumian road directly with Rome.
Gaius Gracchus exerted himself in another way for the improvement of the Italian roads. He secured the due repair of the great rural roads by assigning, on occasion of his distribution of lands, pieces of ground alongside of the roads, to which was attached the obligation of keeping them in repair as an heritable burden. To him, moreover, or at any rate to the allotment-commission, the custom of erecting milestones appears to be traceable, as well as that of marking the limits of fields by regular boundary-stones. Lastly he provided for good -viae vicinales-, with the view of thereby promoting agriculture.
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Reference address : https://www.ellopos.net/elpenor/rome/4-11-commonwealth-economy.asp?pg=22