Ok now still sitting behind the Rostra, look to the right and below the Tabularium's third window, also in front of the Tower and beneath the modern staircase. There you'll see an ugly raised platform made of concrete and rubble (opus caementicium) with a few marble fragments lying around. That is what remains of the Temple of Concord aka Concordia, Concordia Augusta. Concord basically means harmony, agreement. Concordia is a Roman goddess taken from the Greek goddess Harmonia. This Concordia Temple originally was for agreement, understanding and martial harmony. Later (10 AD) when it was rebuilt and became the Temple of Concordia Augusta it was for harmony in the Imperial family.
If you are a fan of HBO's Rome you might recall in the second season when Vorenus calls the heads of the criminal gangs together for a meeting. Priests arrive with a Concordia statue to ensure peace and harmony at this meeting, later Vorenus smashes the Goddess' statue.
Traditionally the first temple was built in 367 BC by M. Furius Camillus This temple celebrated the Licinian Laws which after about 100 year power struggle between the Patricians (aristocracy) and the Plebeians (common people). These Laws gave debt, land and work reform to the poor Plebeians plus a single voice in the government. Many modern historians are skeptical that this 367 BC temple was ever built, and believe that in 218 BC Praetor Lucius Manlius actually built the first Temple of Concord here.
In 211 B.C. the statue of Victory on its roof was struck down by lightning. That temple was completely restored in 121 BC by Consul Lucius Opimius. It is still a conventional rectangular temple 41 m x 30 m. This restoration followed the murder of the Tribute of the Plebians Gaius Gracchus. There was basically a major political mob civil war going on between the Plebians and a Patrician faction. The Plebs lost (3000 executed without trial) and the Senate (Patricians) ordered this Temple restoration to show everyone everything was just A-OK and couldn't be better...Plebs aren't happy, this new restored temple is just spitting in their faces. And for an added kick in the toga: at the same time as this restoration Consul Opimius also builds the Basilica Opimia next to it (on the other side of the modern stairs beneath the present day ground level). Opimius promised any man who brought him Gracchus' head the same weight in gold. Gracchus with the help of his slave killed himself before capture just on the other side of the Tiber. Then some guy just chops off his head and later pours lead in it and cashes it in :-) . A decade earlier in the Forum his older brother Tiberius was killed in a political street fight along with 300 others.
The Roman Senate also meets here on occasion (since 121 BC) and Cicero made his fourth Catiline Speech and possibly another earlier Catiline Speech inside.
On March 15, 44 BC after Brutus and his boys killed Julius Caesar they barricaded themselves in the Temple of Jupiter on the Capitoline Hill. Later in the day they came down and assembled in the portico of the Temple of Concord to address the crowd in the Roman Forum to explain why they killed Caesar. History claims either they did have their say and Brutus spoke or they were forced back to the Capitoline by an angry mob. Cicero although not a conspirator was on their side and supposedly with them there. I assume they chose this temple for its symbolic meaning (harmony, agreement, etc).
OK what we see today is from 10 AD restoration. But much of this concrete core belongs to the 121 BC reconstruction and is probably the oldest known concrete in the city. The only surviving parts are the podium and the threshold of the door of the cella (two huge slabs of pink-grey Chian Marble) and a fragment of the entablature in the Tabularium (look up into the window above and you can see it), and also two column bases and a Corinthian capital are in the Forum Museum but sadly not on display. Also in the podium are two chambers which may have been storerooms for treasure (common in temples).
If you look beneath the window you'll notice the Tabularium's foundation stones are rough-cut compared to the rest of that level. That is because when the Tabularium was built it butted against this 121 BC temple so these stones were unseen and no need to finish-cut them.
And as you can see that earlier temple was narrower than this 10 AD rebuilding. In 10 AD Tiberius (not Emperor yet) with his spoils of war from Germany. And in his name and that of his dead brother Drusus rebuilds, enlarges and dedicates this as the 'Temple of Concordia Augusta' on Jan 16, 10 AD. Now to enlarged this temple within this limited space it's flipped sideways to make it bigger, meaning it's a lot wider than it is deep (45 m x 24 m).
I want you to picture this temple using this coin image and the scant remains that you see at www.uark.edu/ua/metis2/zanker/zanker_fig6.jpg
You'll notice the actual temple foundation remains are in three sections. The lowest is the stairs = that lead up to the columned porch +, this porch like the stairs is narrower than the actual temple . So we have += but what we see is the porch + and the stairs = right alongside that modern staircase so the upper  or right section of the temple is actually beneath those modern stairs.
Now look at the coin photo: At the peak are embracing three figures, most likely the Goddess Concordia flanked by two other female deities who were either PAX (peace) and SALUS (health) or SECURITAS (security) and FORTUNA (good fortune). On each side are statues of Tiberius and his brother holding spears and on each side of them statues carrying the war booty (armor and trophies). This was public relations for Tiberius saying "I personally built this with the booty from my victorious German war". And at each end a statue of Victory. The statues on the staircase are of Hercules representing security in the Empire and of Mercury prosperity in the Empire. Inside the temple you can see the seated statue of the Goddess Concordia.
The blank pediment in real life would have had sculptures within. Also on the temple's threshold inlaid in bronze was Mercury's Wand (caduceus) which was an emblem of peace.
Tiberius in reality made this now beautiful temple into a museum/temple. Inside were some of the greatest works of art of the time (mostly Greek sculpture and panel paintings) along with other ancient treasures. The greatest treasure within was the sardonyx (onyx/gem) signet (a seal ring) that was thrown into the sea by the pirate-ruler 'Polycrates of Samos' (about 540 BC) as an offering to Fortune, only to have it returned (rejected) later in the belly of a fish and dooming the tyrant. It was given to the temple by Livia Augustus' wife and was kept in a golden horn.
Emperor Augustus also gave the temple four elephants carved in Obsidian (black volcanic glass).
It's believed the last rebuilding of this temple was after the 284 AD Fire.
For more information and photos, please see Temple of Concord in A Tourist in Rome.Next: #12.3: Temple of Vespasian and Titus