Ok now, look across the Via at the intact round building with bronze doors shown here. This Temple and the Pantheon are the only two intact Pagan Temples in Rome both saved because the Christians took them over and this one was used as a Vestibule into the Christian Church behind it.
But what this Pagan Temple was built for and called in ancient times is still a mystery. It is either one of four different possible temple scenarios or we just really don't know.
We'll start with what they have called it for centuries, the 'Temple of Romulus'. Pagan Emperor Maxentius (a usurper Emperor 306-312 AD) was defeated by Constantine (he saw the cross or some Christian symbol in the sky, defeated Maxentius and became the first Christian Emperor in 312). Emperor Maxentius' son (Romulus) died in 309 at age four and was deified as a God. It was believed by Mediaeval sources that this Temple was built by Maxentius in memory of his son and other recently deceased members of his family.
This was mainly based on two different 310 AD coins Maxentius put out in memory of his son which shows a round building somewhat like this Temple, but his son's very large mausoleum out on the Via Appia Antica (near the Catacombs) is also round. So it's a questionable comparison today by many historians/archaeologists who often call it "The So-Called 'Temple of Romulus'".
(1) Many historians and archaeologists believe that it is actually a 'Temple of Jupiter Stator' built by Maxentius at the place it has always been for centuries or just possibly reinstated at its original location. Maxentius and the Pagans are losing ground to the Christians (estimates of about 25% of the Empire is Christian and rising) so he is reviving a lot of the old original Pagan Gods and Temples. Plus he named his son after Romulus. In this case (if so), remember Romulus in 753 BC gets knocked out in battle and his troops then retreat heading towards the Palatine, he quickly revives and calls to the God Jupiter for help and then suddenly his troops are immobilized and can't move on the Via Sacra. And then the spell is lifted and they return to the battlefield at the Roman Forum marsh. And later Romulus builds an outdoor Altar to Jupiter at the place where he called out to the God to "Stay" (Stator) his troops.
(2) It's the 'Temple of the Penates'. Roman household Gods who protected the family and worshipped privately in the home but they were also worshipped with Vesta and Lares in public on behalf of the whole community. This Temple hasn't been heard about since Augustus' time and possibly was destroyed in the 64 AD Fire and not rebuilt. And this was possibly one of the Pagan Cults Maxentius brought back?
(3) It actually was an original short-lived 'Temple of Romulus' built two years before Constantine beat Maxentius and when Constantine became Emperor the Temple was renamed something else.
(4) Maxentius built this Temple on the site of the 'Temple of Jupiter Stator' but renamed it 'The Temple of Romulus' after his son. Two years later Constantine renamed it back to the 'Temple of Jupiter Stator' and removed anything related to Romulus or Maxentius.
I go with #1 or #4. It was always the Jupiter Stator Temple except for perhaps two years (310-312 AD). Because the modern two scholars at the *Very Top* of the food chain for this type of identification believe It Is. Adriano La Regina, Head of Rome's Archaeology Department for 24 years and many other major things (Professor, author, etc) in this area. And Major League Italian archaeologist Filippo Coarelli (Professor, author, etc).
[Hopefully I've gotten this accurate for both of them] Because based on its Via Sacra location, the City's ancient small administrative regions, ancient authors' writing of nearby monuments in that "region", etc this is the most logical place for this Jupiter Stator Temple. Plus I assume having no records what the Temple was originally Named in 310 helps this case also as it can't be definitely identified as something else? Although History has always wanted to place this Stator Temple near the Arch of Titus I believe only based on something Plutarch wrote? (ancient authors are known for getting things wrong sometimes). Plus that Arch location is in the wrong "administrative region" and also not the right location in regards to the other known nearby building locations other ancient authors mention.
The whole temple structure is constructed of brick faced concrete and the Temple's round dome is concrete. The building was faced in marble slabs (likely looted). Everything fancy that you see (door and frame, columns, bases, capitals, etc) was looted from older buildings.
Rome is the Western Roman Empire and it's fallen on very hard times and about 160 years later it's the 'Fall of Rome'. Constantinople is the Eastern Roman Empire and they're doing just fine and they don't Fall for another 1100 years or so.
First note the height of the doorway, that was the ground level in 310 AD when this Temple was built. The bronze doors and marble frame are from about 200 AD and the door's keyed lock still works even today. Surrounding the door frame: The top cornice is three blocks, two from an Augustian-era building and the middle one was made up for this building. There are holes on top of this cornice so there was a pediment ^ attached above it either here or at its original location. The next cornice has four blocks: the middle two are from the first and second Century and the end ones are made up. The Architrave has a plant scroll decoration that was meant to be seen vertically not horizontally first Century AD. The two red columns are of slightly different lengths and their Corinthian capitals are about 90 AD.
The round temple has a Hall on each side which opened out to the Via Sacra. The left Hall is mostly gone but the right Hall one is somewhat intact with two green columns. One column has a Corinthian capital about 90 AD with a cornice block on top about 200 AD with two made up sections between them.
Originally the two Halls were squared-off with the round temple [`]O[`] but Constantine added a curved wall on each side of the Temple door (more visually appealing) with a large niche in each that was later walled up. In the sixteenth Century part of an inscription (now lost) on the facade was recorded for 'Constantine the Great' (Maxentius's name would have been removed if it was ever on there at all).
In the Temple's exposed foundation there are a couple of small drains with triangular cover and a section outlined by terracotta slabs that mark a Medieval burial area.
The Temple is sometimes open (only started a year or so ago) but you can also view it from a window inside the Church behind it (Santi Cosma e Damiano).
Inside the Temple were doors to the side Halls and a wide door in the back opened into a large rectangular audience Hall (now that church) which then lead into the very much larger 'Temple of Peace' (Built by Emperor Vespasian 70 AD but by the fourth Century it's called the Forum of Peace likely because it became a food market), that Hall was also part of this Temple/Forum. So now this 310 AD Temple is also monumental entrance into the large audience Hall. And two centuries later the Temple of Romulus is saved from destruction because that audience Hall is turned into a Church (527 AD) and the Temple becomes the vestibule of that Church.
For more information and photos, please see Temple of Romulus in A Tourist in Rome.Next: #30: Sacellum of Bacchus