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
The migration of the Umbrian stocks appears to have begun at a period later than that of the Latins. Like the Latin, it moved in a southerly direction, but it kept more in the centre of the peninsula and towards the east coast. It is painful to speak of it; for our information regarding it comes to us like the sound of bells from a town that has been sunk in the sea.
The Umbrian people extended according to Herodotus as far as the Alps, and it is not improbable that in very ancient times they occupied the whole of Northern Italy, to the point where the settlements of the Illyrian stocks began on the east, and those of the Ligurians on the west. As to the latter, there are traditions of their conflicts with the Umbrians, and we may perhaps draw an inference regarding their extension in very early times towards the south from isolated names, such as that of the island of Ilva (Elba) compared with the Ligurian Ilvates.
To this period of Umbrian greatness the evidently Italian names of the most ancient settlements in the valley of the Po, Atria (black-town), and Spina (thorn-town), probably owe their origin, as well as the numerous traces of Umbrians in southern Etruria (such as the river Umbro, Camars the old name of Clusium, Castrum Amerinum). Such indications of an Italian population having preceded the Etruscan especially occur in the most southern portion of Etruria, the district between the Ciminian Forest (below Viterbo) and the Tiber.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/1-08-umbro-sabellian-samnites.asp