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
Akin to this was the development of the form of the round temple with the dome-shaped roof, which was foreign to the Greeks, but was held in much favour with the Romans and was especially applied by them in the case of the cults peculiar to them, particularly the non-Greek worship of Vesta.(37)
37. The round temple certainly was not, as has been supposed, an imitation of the oldest form of the house; on the contrary, house architecture uniformly starts from the square form. The later Roman theology associated this round form with the idea of the terrestrial sphere or of the universe surrounding like a sphere the central sun (Fest. v. -rutundam-, p. 282; Plutarch, Num. 11; Ovid, Fast. vi. 267, seq.). In reality it may be traceable simply to the fact, that the circular shape has constantly been recognized as the most convenient and the safest form of a space destined for enclosure and custody.
That was the rationale of the round θησαυροὶ of the Greeks as well as of the round structure of the Roman store-chamber or temple of the Penates. It was natural, also, that the fireplace--that is, the altar of Vesta--and the fire-chamber--that is, the temple of Vesta --should be constructed of a round form, just as was done with the cistern and the well-enclosure (-puteal-).
The round style of building in itself was Graeco-Italian as was the square form, and the former was appropriated to the store-place, the latter to the dwelling-house; but the architectural and religious development of the simple -tholos- into the round temple with pillars and columns was Latin.
Something the same may be affirmed as true of various subordinate, but not on that account unimportant, achievements in this field. They do not lay claim to originality or artistic accomplishment; but the firmly-jointed stone slabs of the Roman streets, their indestructible highways, the broad hard ringing tiles, the everlasting mortar of their buildings, proclaim the indestructible solidity and the energetic vigour of the Roman character.
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Reference address : https://www.ellopos.net/elpenor/rome/2-09-art-science.asp?pg=39