He was also interested in trying to re-create Classical antiquity to honour himself, such as his creation of a Triumphal Arch at Capua - also known as the Capuan Gate. Elsewhere Frederick had incorporated Roman remains and architectural members into his castles, but here he tried to create his own Classical monument.
The arch marked the point where the via Appia and the via Latina met, two ancient roads that were still in use, and by making the arch incorporate the city gate of Capua he forced all to pass through it and acknowledge his supremacy. The Arch was built in 1234-9, but destroyed by the Spanish in 1557. Our best evidence for its appearance is this manuscript from 1507 now in Vienna (Man. 3528, folio 51, verso), and the many pieces of sculpture now in the Museo Campano of Capua (they reconstruct it as below, source).
Frederick himself was shown seated, in the center of the monument, in Roman dress as can be seen in the image below (source):
cod. Vat. Lat. 9840, foglio 50r), but it was also depicted on his coins and on a gem.
source), personifications of cities being a Roman concept, or more specifically of Frederick's Justice to Capua, according to the inscription below her:
Caesaris imperio regni custodia fioThe men framing her were inscribed "Intrent securi qui quaerunt vivere puri" and "Infidus excludi timeat vel carcere trudi"
Quam miseros facio quos variare scio
More sculptures from the Arch can be seen here and here
Although the larger sculptures were contemporary, some of the smaller ones were Roman, mostly Hadrianic, and possibly recycled from the town's amphitheatre. More Roman fragments were used as spolia within the city walls.
The road that went through the arch was built to a Roman standard, making it almost three times the normal width in use at the time. Even the capitals the arch sprang from were carved like Corinthian capitals (source):
source) It shows how Frederick II saw himself, as the heir of the Roman emperors and one of them.
early Byzantine emperors in Constantinople, Frederick II and his father Henry VI were entombed in imperial porphyry sarcophagi in Palermo cathedral. The porphyry quarries in Egypt had long been lost, so he must have had Late Antique sarcophagi shipped from Rome and re-carved - this was no easy feat, given that the stone was so hard some emperors had much plainer ones, and shows how determined he was to be buried in the imperial fashion. But then again Frederick, like Constantine, thought he was above the pope and showed he was not afraid to take on Rome. So even in death he was a Roman emperor.
Perhaps the greatest testament to Frederick is the inclusion of his chief advisor Pier della Vigna in Dante (Inferno XII), where he describes Frederick as "Caesar" and "Augustus" and as much a Roman as a Christian. This was heresy to Dante, but would have been music to Frederick's ears.
Cast of a Silenus head used as on a keystone at Castel del Monte
Cast of a cavalry frieze re-used at Castel del Monte