From Via dei Fori Imperiali to the Colosseum
The valley where the Roman Forum came into existence was formed by the Tiber's erosion of the sides of the volcanic lava from which the seven hills originated.
Towards the end of the 6th century BC, under the Tarquin dynasty, the valley was reclaimed and the waters drained into the Tiber down a sewer, the Cloaca Maxima. As such, the area was now ready for use by the tribes who were already living on the surrounding hills, providing them with a place to meet, exchange goods and carry out the main activities of daily life. Thus, the Roman Forum was born, and became the centre stage of Roman history throughout the period of the Republic, right down to the 1st century AD.
During Nero's reign, the area currently occupied by the Colosseum constituted the fulcrum of his Domus Aurea complex. In particular, the area where the amphitheatre lies was previously an artificial lake that was reclaimed after the emperor's death to construct the new, grand monument. The monument's actual name is the Flavian Amphitheatre because it was built by the Emperor Flavius. Its current name, the Colosseum, is most likely in memory of the nearby colossal statue of the emperor Nero.
At the end of the Republic period, the ancient Roman Forum was no longer able to perform all of its necessary functions. By this time, Rome had become the centre of an true Empire and needed to increase its practical space. The most appropriate space for such purpose was identified as the area to the northwest of the former square.
For centuries an intricate labyrinth of streets, shops and markets existed in this area. Julius Caesar was the first to intervene by creating the Forum of Caesar, which became the "prototype" for the Imperial Forums. Augustus followed Caesar's example by adding another Forum perpendicular to the existing structures and penetrating deep into the heart of the Suburra. Then, it was Vespasian who created the grand complex to the south known as the Temple of Peace in order to celebrate his Judean conquest and it actually served as a public square.
Between this complex and the preceding Forum of Augustus, there was a narrow space which Domitian used to create the so-called "Transitory Forum." These forums were actually completed by his successor Nerva and took his name. When Trajan finally rose to power, the remaining area was deemed insufficient in size for his conquests. Thus, Trajan decided to excavate the area that joined the Campidoglio with the Quirinal Hill in order to create the space necessary to build the longest, largest and most spectacular of them all, the Imperial Forums.
Must see: the Roman Forum; The Arch of Costantine; The Colosseum; The Temple or the Forum of Peace; The Forum of Nerva; The Forum of Augustus; The Forum of Trajan.