Elevated three steps above the courtyard, which was paved in white marble, the columns of the porticoes that ran the length of the forum were of yellow giallo antico and supported a coffered entablature surmounted by an attic again in white marble decorated with caryatids. This contrasted with the floors of the temple and porticoes, which were a combination of colored marbles.
In the model above, one can better imagine the arrangement of the forum. Along the back wall of the colonnade were a series of niches framed by engaged columns that held statues of the Julian clan and the summi viri of Rome, each with an inscription recording his accomplishments.
"Next to the immortal Gods he honoured the memory of the leaders who had raised the estate of the Roman people from obscurity to greatness. Accordingly he restored the works of such men with their original inscriptions, and in the two colonnades of his forum dedicated statues of all of them in triumphal garb, declaring besides in a proclamation: 'I have contrived this to lead the citizens to require me, while I live, and the rulers of later times as well, to attain the standard set by those worthies of old'" (Suetonius, Augustus, XXXI.5; cf. Dio, LV.10.3).
Given the irregular dimensions of the back wall, there was room at the end of this portico for a separate hall, which contained a colossal statue of Augustus (Martial, VIII.44), possibly placed there by Claudius or Tiberius, the imprint of the foot still visible. It is here, between the pilasters, that paintings of Alexander the Great by Apelles (Pliny, XXXV.27) may have been placed (Servius, Aeneid, I.294), an association with the emperor that was made even more deliberate by Claudius, who later cut out the face of Alexander and substituted a portrait of Augustus (Pliny, XXXV.94).
In fact, it is not possible to know with certainty how the statues of the summi viri were arrayed around the exedrae and porticoes. Suetonius implies that they were placed in both porticoes of the forum, Dio that "such victors and all others who receive triumphal honours should have their statues in bronze erected in the Forum" (LV.10.2), and the Scriptores Historiae Augustae that Augustus "erected in his forum marble statues of the most illustrious men, together with the record of their achievements" (XXVIII.6). The names of Spain and other Roman provinces also were displayed (Velleius, II.39.2).
The detail above is from a wood and plaster model of the forum in The Museum of the Imperial Forums in Trajan's Market (Rome). Constructed in 1937 by Italo Gismondi, who also built the model of Rome, it is 1:50 scale.
References: Suetonius: The Lives of the Caesars (1914) translated by J. C. Rolfe (Loeb Classical Library); Scriptores Historiae Augustae (1924) translated by David Magie (Loeb Classical Library); Velleius Paterculus: Compendium of Roman History (1924) translated by Frederick W. Shipley (Loeb Classical Library); Dio Cassius: Roman History (1914-) translated by Earnest Cary and Herbert B. Foster (Loeb Classical Library).
