There is an etching of the Forum of Nerva when it was still complete.
http://classics.furman.edu/~rprior/imgs/RCU2/2-151.jpg
Although the statues that topped the walls are probably among the many loose heads, arms, and torsos that collect in Rome's museums, one can get a sense of the kind of lush detail that the place possessed.
The Forum of Nerva was dedicated to Minerva. The reliefs depict the lives of women in Rome.
The largest of the Imperial fora was the Forum of Trajan. It was probably begun at the same time as the Forum of Nerva, by the Emporer Domitian, but it had to be carved into the side of the Capitoline hill to make it level with the other fora. It was the last forum to be completed, around 112 or 113 A.D. At its completion this forum had five levels of shops.
Excavation continues in this area, unearthing bits of column and engraving.
Bit by bit, though, it is being reconstructed.
The patchwork appearence of the columns isn't all reconstructive efforts, though. By this time the columns were often made of brick, with a marble facade. Presumably this was easier and/or cheaper than erecting pure marble columns.
Marble relief statues, recovered but not yet replaced. Once, the far wall of this forum was a monumental relief statue of the emporer on horseback.
One of the many cats that reside in the Roman ruins, sunning his belly.
The Trajan column is the most striking feature that remains of the Imperial fora. It is nearly 100 feet (30m) tall. It was originally topped with a statue of a bird, then one of Emporer Trajan, and now bears a statue of Saint Peter, an addition of the Catholic church in 1588.
The entire column is carved with reliefs depicting battles in the war with Dacia, the spoils of which were used to fund the construction of Trajan's forum. The column consists of 18 wheels stacked on top of one another, and the interior of the column is a spiral staircase leading to the viewing platform at the top. The platform is about 4m across. Notches in the stones give hints as to how this enormous structure was built - one can imagine levering the stones with huge beams of wood. Traces of pigment have been found on the column as well, implying that at least for a time the reliefs were painted.