Imperial Forums
The Imperial Forums consist of a series of monumental fora (public squares), constructed in Rome over a period of one and half centuries, between 46 BC and 113 AD. The forums were the heart of the late Roman Republic and of the Roman Empire.
The Imperial forums are not part of the Roman Forum, which was the public square during the Roman Republic. These forums were the centres of politics, religion and economy in the ancient Rome.


Forum of Caesar
Julius Caesar decided to construct a big forum bearing his name. This forum was inaugurated in 46 BC, even if it was probably still incomplete at this time and was finished later by Augustus.
The Forum of Caesar was constructed as an extension to the Roman Forum. The Forum was used as a replacement venue to the Roman Forum for dealings in public affairs as well as the noblest activities; it was also designed as a celebration of Caesar's power. Caesar had placed, on the front of his forum, a temple devoted to Venus Genitrix, since Caesar's family (gens Julia) claimed to descend by Venus through Aeneas; a statue of Caesar himself riding Bucephalus, the celebrated horse of Alexander the Great, was placed in front of the temple, to symbolise absolute power. This centralised vision corresponded to the ideological function, following the propaganda of the Hellenistic sanctuaries; also the choice of the Forum site carried a meaning: the future dictator didn't want to be far from the central power, represented in the Curia, seat of the Senate. In fact, not long before Caesar's death, the Senate agreed to reconstruct the Curia on the site.

Forum of Augustus
In the battle of Philippi in 42 BC, in which Augustus and Mark Antony worked together and avenged Caesar's death, Augustus vowed to build a temple dedicated to Mars Ultor. The incomplete forum was inaugurated, after 40 years of construction, in 2 BC, adding the second monumental square, the Forum of Augustus.
This new complex lies at right angles to the Forum of Caesar. The temple consists of a very tall wall, and this still distinguishes itself from the popular neighbourhood of Suburra. The rectangular square has long deep porticos with a surface that widens into large semicircular exedras.
The entire decoration of the Forum was tightly connected to the ideology of Augustus. According to myth, Rome herself was born from the god Mars through Romulus.

Temple of Peace
In 75 AD, under Emperor Vespasian, another great square was built. Separated from the Forum of Augustus, the Forum of Caesar, also separated from the Via dell'Argileto which connect the Roman Forum to Suburra, the temple was opened to the Velia hills (in the direction of the Colosseum. The fact that this structure is not mentioned as having a civil function has prevented it from being classified as a true Forum. Therefore the structure was simply identified as the Temple of Peace (Templum Pacis) until the late Empire.
Also the shape of the square was different: the temple was constructed by a large apsidal hall that opened up like an exedra at the bottom of the portico. A row of columns distinguished the portico from the temple. The centre area was not paved like other forums, and it served as a garden, with pools and basements for statues, so that it was similar to an open air museum.
The monument was built to celebrate the conquest of Jerusalem. One of the chambers opened at the end of the porticos housed the Forma Urbis Romae, a marble map of antique Rome, made in the Severian period (3rd century) by drawing on the marble slab that covered the wall.

Forum of Nerva, or the Transitional Forum
Domitian decided to unify the previous complex and the free remaining irregular area, between the Temple of Peace and the Forums of Caesar and Augustus, and build another monumental forum which connected all of the other forums.
The limited space, partially occupied by one of the exedras of the Forum of Augustus and by the via dell'Argiletto, obliged Vespasian to build the lateral porticos as simply decorations of the bounding walls of the forum. The temple, dedicated to Minerva as protector of the emperor, was built leaning on the exedra of the Forum of Augustus, so that the remaining space became a large monumental entrance (Porticus Absidatus) for all the forums.
Because of the death of Domitian, the forum was inaugurated by his successor, Nerva, who gave his own name to the forum. The Forum of Nerva is also known as Transitional Forum, because it worked as an access way, just like via dell'Argileto had done.

Forum of Trajan
It is probable that Domitian's projects were more ambitious than the building of the small "Forum of Nerva", and probably under his reign they started to remove the small saddle that united the Capitoline Hill to the Quirinal Hill, thus blocking the Forums towards Campus Martius, near to modern Piazza Venezia.
The project was taken back by Trajan with the construction of Trajan's Forum between 112 and 113. The occasion was the conquest of Dacia, whose spoils paid for this celebration of the military conquests of Rome.
The preparation of the Forum required a lot of work. It was necessary to remove the hilly saddle, and to support the cut of Quirinal Hill through the building of the Trajan's market. The Forum square was closed by the Basilica Ulpia, with Trajan's Column at its back. In front of the basilica, a monumental façade was the background of a large, equestrian sculpture of the Emperor. The last Forum was also the biggest and greatest.


From: www.wikipedia.org