Ok now, why don't you walk back over to behind the Rostra and have a seat with your back to the Rostra and Forum. I'm labeling the next five sites #12.1, 2, 3, 4, 5 because you can do them while sitting there and relaxing :-) .
In front of you is a large multi-storied building. It has a ground level (basement) with six windows, and a first floor with three large arched openings. Now those two levels are ancient but built over the first floor is a modern looking structure consisting of three shorter floors. I will call that entire three-floored section the second Floor as it is not original to the building but this building did have a second floor in ancient times.
*Today* they call this ancient building the 'Tabularium' which literally means 'a place usually a room or cupboard for storing 'Tabula' (writing tablets). In this case it's a building. But they really don't know what the ancient Romans actually called this building nor are they a 100% certain as to what purpose it actually served.
The modern name is based on an inscription that was *seen* in the fifteenth Century in the basement (now lost but the inscription was recorded). It said that the "Consul of 78 BC Quintus Lutatius Catulus (General/Dictator Sulla's Lieutenant) commissioned the building of a Substructio (basement) and a Tabularium (very likely meaning an upper floor or floors)". Remember this inscription was just *seen* in the basement which strongly hints that it was just *found* there (originally mounted elsewhere but over the centuries ended up here?). Because no Roman would ever mount their dedication plaque in a basement where it couldn't be seen by their peers and the common people! Anything like this was always good personal public relations and bragging was very much expected. The Inscription's date and the date of this building are very close plus a basement and an upper floor(s) fits the bill.
A second inscription to him was found in the Forum in 1845 but doesn't really connect him to this *exact* building. This inscription can be seen on the right side (N) of this building facing the Via di San Pietro in Carcere. It's a keystone over a doorway: [Q · Lu]tativs · Q · f · Q · n · C[atulus Consul] · cos · [de · s]en · sent · faciundu[m · coeravit ·] eidemque · prob[avit].
So it's the popular opinion that this building was a 'Public Records Office' which also housed some government offices. Even though there is no record of any such building existing. So we'll just follow the herd on this :-) .
The Tabularium was commissioned by Consul Q. Lutatius Catulus and designed by the architect Cornelius in 78 BC. It stored public records like deeds, laws, treaties, Senate Decrees, etc and also housed government offices. The upper half is the Palazzo Senatorio where today Rome's City Council meets and the Mayor has his office. In the eleventh Century a fortress was built atop the Tabularium and the Senate probably starting meeting here about 1150 AD. Later in the thirteenth Century a palace fortress with four towers was built, these towers also strengthen this ancient structure. The tower you see on the right has Pope Bonifatius IX 'Coat of Arms' (1398) on the tower. In the sixteenth Century Michelangelo removed the ancient second floor and built the upper floors we see today.
The original Tabularium was trapezoidal and over 3000 square meters and it roughly follows the present day building's shape. It was a pretty impressive building overlooking the Forum but that was short lived. The Temple of Concord always blocked part of it on the right side and more later on when the temple was enlarged. And about 150 years later the Temple of Vespasian and Titus was built directly in front of it blocking it even more.
Ok let's start at the BASEMENT LEVEL: There was once something here (in the center to center-left) before the Tabularium was built but we don't know what that building was. This basement has six small windows and rooms with a corridor running its length. Access was by an internal staircase at the Northern end. The basement is made up of that wall you see on your side and on the inner-side it was cut into the tufa rock of the Capitoline Hill. The Wall is made of Tufa blocks of stone 2 x 2 x 4 Roman Feet. The stones are laid with one row long _____ and the next row short ------ and is called Opus Quadratum. They are also cemented together with a thin layer of cement. If you look to the right end section of that Wall you will notice the blocks aren't finished smooth but left rough cut. That is because the Temple of Concord of which only the base foundation and some fragments survive blocked that section from view. It's not known what the basement rooms were used for but they were later used as a prison right up until the nineteenth Century. And at some point in later history salt (a state monopoly) was stored in this building which caused some corrosion to the interior.
FIRST FLOOR: This floor has three large arched windows. Originally that whole floor facing you was made up of eleven arched windows, they were covered-over in the Middle Ages when this was made into a fortress (about 100 years ago only one window was open). You can see this cover-up to the sides of the left and the middle arched windows. This floor was actually just a higher level pedestrian gallery/passageway connecting the two higher peaks of the Capitoline Hill o====o and not used for any functions of the Tabularium behind, above or below it. The half columns you see beside the arched windows are Doric, their capitals and architrave are white Travertine limestone with a Doric frieze of metopes and triglyphs.
SECOND FLOOR: In the sixteenth Century Michelangelo took out the ancient second floor and built the upper level building we see today. The second floor was either a late first Century AD restoration of the original or was an addition. Fragments found in the area show the second floor was Corinthian entirely in Travertine and dated to the Flavian Era (late first Century). Its height would have been to just below the second row of modern windows we see today. And it was an open gallery with arched windows just like the first floor.
If it is not a Monday you will see tourists in the three arched windows on the first Floor. You can visit that floor from either of the Capitoline Muesums on the Capitoline Hill. Here are the directions and info: Go to en.museicapitolini.org/collezioni/percorsi_per_sale/tabularium and scroll down to the plan/map of the Tabularium.
#1 is a modern basement corridor that connects the Capitoline Muesums (Palazzo Nuovo and Palazzo dei Conservatori). This corridor is also a mini-museum with bathrooms and a wheelchair stair lift. But sadly to get into the Tabularium section there are stairs.
#2: At the top (or bottom) of the stairs leading up from this museum-corridor is the colossal marble statue of Veiovis found in the Temple of Veiovis which very likely was the cult statue that was worshipped in the Temple. This Temple is shown on the map in the center as a rectangle of dotted lines -----. This marble statue very likely replaced the original 300 year old cult statue that was made of cypress wood and possibly was destroyed in the Major 80 AD Fire. VE-JOVIS; JOVIS is Jupiter and VE is a prefix that means Negative or Diminutive Value. So in the beginning he was sort-of an Anti-Jupiter, later he left the 'Dark Side of the Force' :-) and just became a 'Young Jupiter'.
The temple was vowed in 196 BC but by who is unknown and dedicated in 192 BC. Originally it was a typical rectangular temple but when the Tabularium was built it was rebuilt sideways for space-saving and enclosed by the Tabularium on two sides. In the late first Century AD brick piers were added to the cella walls probably to support a concrete roof (original was likely wooden). Now on the right-hand side of the corridor at the top of the stairs is a little walk-in nook. Behind the glass you can see the rear portion of the high travertine marble pedestal of the Temple of Veiovis and beyond the remains of the large tufa-stone Tabularium wall which was indented to allow for the presence of the temple.
At the end of this #2 corridor leading to #3 on the right-hand side is a section of the entablature from the nearby Temple of Vespasian and Titus. This entablature shows sacrificial instruments and dates to the original Temple (80-85 AD).
#3 Is the section with the three large arched windows overlooking the Forum with great photo ops. Now as soon as you enter this long gallery look to the left and up. That large marble fragment (first Century AD) is an architrave from the Temple of Concord which is right below that first arched window (the Temple Vespasian/Titus was just to the right of it). Also above you is the best example of the pavilion vaults that made up the roof of this long gallery. Remember this gallery was made up of eleven arched windows not just the three you see today. The archways were walled up in the Middle Ages when this was turned into a fort. And right up until recent times only one archway was open (I think it might be the first one?). In the middle of this gallery if you see a small plexiglass section that covers an air vent for a basement water main (late first Century).
#4 Is halfway down the gallery and is a large high open room where you can look into the basement. The partial floor paving you see is from the Republican Era (pre-44 BC). Other floor remains are from a building that predates the Tabularium also that metal grate covers a cistern that was lined in Opus Signinum. Also in one of the three rooms is a mosaic floor (white background with irregular chips of colored marble) that is the oldest in Rome (second half of second Century BC). And you can see one of the six windows of the basement level.
For more information and photos, please see Tabularium in A Tourist in Rome.
Next: #12.2: Temple of Concord