The construction of the Temple of Mars must have been promoted by Stilicho soon after his victory against Radagaisus: let’s say around October-November of 406, while its conclusion is indicated by a mission of Florentines who went to ask Emperor Honorius permission to remove his statue, mission which can be posed no later than August of 423, the date of his death.
Thus in 423 the statue was in its place, and the Florentine Christians wanted to use the Temple as a church: this means that at least the rough construction was completed, and in the interior flooring and claddings were also done. Therefore, the construction lasted 17 years, to which a few years can be added because they still had to carry out the external claddings, or, if not all, then at least a part of them, given that the marbles of the corner pillars were posed only in 13th century. In total, thus, we can calculate little more than twenty years for the construction, which is a possible but rather short timeframe, because in the calculations not only should the duration of the work be understood, but also the time necessary for the preliminary agreements to be made, the design to be drawn up, the search for the architect to head the project, as well as the stipulations of the contract should be factored in.
If these preliminary phases were short, it means that the channels activated in Rome, and which are spoken about in the chronicles, worked to perfection, and if the building proceeded speedily regardless of the distance from which the worked marbles arrived, we can deduce a great organization of the contractors. Fruit of centuries of experience, that organization allowed them to restrict the timeframe and optimize the chain of production, transportation and assembly of the marbles, and work in Florence on the rough walls while at the quarries (which I believe were in the Aegean region, between Greece and Turkey) they prepared the marbles.
But the design had to precede the work, not overlapping on it, and for the drafting of such a perfect and detailed design three to four years could be estimated, which should be taken out of the calculated twenty, and so it would critically be constricted the building timeframe.
And then?
Then there are two hypotheses, not necessarily alternative, and both plausible and consistent with the historical context.
One is that we are facing an entrepreneurial feat made necessary by the disastrous situation of the public contracts: a construction company couldn’t miss this kind of opportunity, so every record was broken.
The other, is that the Florentines bought a pre-made package of design and marbles; and this would be a rather fascinating case, but with a good probability of being well-founded.
Could someone have needed a similar monument earlier and then not begun the commission?
Yes, it is possible and actually probable: the same Stilicho four years earlier celebrated another great victory of his when he pushed back Alaric’s barbarians in Pollenzo in 402 and erected a triumphal arch in Rome. Here we would need to open up a parenthesis on the personal events of Stilicho in those years, but let’s only say that he had a lot of enemies in the Senate that wanted him dead; and in fact, in 408 he was killed in a plot that did not spare his son, his wife, his friends, his proteges, his soldiers. A damnatio memoriae followed [that’s to say the total erasure of all memory of a person’s existence], because of which we don’t know much about his triumphs, but some traces on the subject remain. It is therefore possible that some initiative of his was left halfway done, and that he brought it to completion on this other occasion and shortly after the former, thanks to the Florentines.
One final observation should be made regarding the date of 436 as the completion of the construction that the old historian Filippo Buonarroti records having found written it in a note now lost. This date would add another dozen years to the calculations we made: how can we explain it?
An explanation could be that the note may have been referring to the completion of the work of transforming the building into a church, and it is also imaginable that the Florentine Catholics would have lost some time in gathering the funds necessary to make the transformations by using a kind of crowdfunding, given that there was no hope of any public financing.
Thus, in conclusion, it would not be a coincidence if the architecture of our baptistry had such absolute and ideal shapes, because in all likelihood it was designed to be placed in whatever space there was available to celebrate the glory of Rome. Here in Florence, it only needed a few adjustments – about which I believe there remain a few traces – and everything would fit into place.
And it would come as no surprise that the solar meridian didn’t work: according to very recent studies by Gabriele Casetta, in fact, it would have been calculated on the basis of the inclination of the solstitial sunbeams precisely at the latitude of Rome [1]. [1].
[1] G. Casetta, “The Baptistry of Florence – A Liturgical and Symbolic Reading” – thesis defended at the Pontificio Ateneo Sant’Anselmo in Rome a.a. 2021, p. 128 (unpublished).
The source areas of the marbles of the Baptistry.