Ancient Roman Forums
The Roman forums were public buildings about three times as long as they were broad. All the compass of the forum was surrounded by arched porticos with some passages being left as places of entrance. (A portico is a porch that leads to the entrance of a building with a roof structure supported by columns or enclosed by walls, such as the portico of the Pantheon). The Ancient Roman Forums were the centres of civic, religious and economic life in the city. The most remarkable of the Ancient Roman Forums was the Roman Forum, built by Romulus, and adorned with porticos on all sides, by Tarquinius Priscus. This was the most ancient and most frequently used in public affairs.

Ancient Roman Forums - Imperial Fora
Imperial Fora, Rome - Fora meaning public squares: The Imperial Fora were a group of Forums built by the Roman emperors around the Roman Forum beginning with the Julian Forum begun c54 B.C. and ending with the Forum of Trajan. The Ancient Roman Forums of the Imperial Fora generally had colonnades (porticoes) along their long sides with a podium temple capping the Forum opposite to the entrance on one of the short sides.  

Types of Ancient Roman Forums
There were two kinds of forums, the fora civilia and fora venalia. The first were designed for the ornaments of the city, and for the use of public courts of justice. The other was erected for the necessities and conveniences of the inhabitants, and were no doubt equivalent to our markets. The most remarkable were the Roman forum, built by Romulus, and adorned with porticos on all sides, by Tarquinius Priscus: This was the most ancient and most frequently used in public affairs.

Ancient Roman Forums - The Julian Forum
The Julian forum was built by Julius Caesar, with the spoils taken in the Gallic war; the area alone, cost one hundred thousand sesterces. The "Julian Forum" was begun by Julius Caesar in 54 BC and finished by Augustus. The first of the Imperial Fora, it established the format of the Ancient Roman Forums. They had colonnaded porticoes flanking a podium temple which was opposite the entrance. The temple in the Julian Forum was dedicated to Venus Genetrix (Venus the progenitor) because the Julian family was descended from Venus.

Ancient Roman Forums - The Augustan Forum
The Augustan forum, built by Augustus Caesar c42BC, contained statues in the two porticos, on each side of the main building flanking a Corinthian podium temple of Mars Ultor (Mars the Avenger). This commemorated the avenging of Julius Caesar's assassination. In one were all the Latin kings, beginning with aeneas and in the other all the Roman kings, beginning with Romulus, and most of the eminent persons in the commonwealth, and Augustus himself among the rest, with an inscription upon the pedestal of every statue, expressing the chief actions and exploits of the person it represented.

Ancient Roman Forums - The Forum of Trajan
The forum of Trajan, erected by the emperor Trajan, with the foreign spoils he had taken in the wars; the covering was all brass, and the porticos were exceedingly beautiful. This huge Forum was built west of the Forum of Augustus by Trajan 106-113. The architect was Apollodorus of Damascus. The Forum of Trajan included the Basilica, two libraries, and Trajan's column. The Temple of the Deified Trajan was attached to the complex behind the column by Hadrian. Behind the Forum were Trajan's markets which were a large complex of vaulted brick-faced concrete shops and a Market Hall. The chief fora venalia or markets, were boarium, for oxen and beef, suarium, for swine, pistorium, for bread, cupedinarium, for dainties, and holitorium, for roots, salads and similar things.