There's very little left apart from the toppled Triumphal Arch scattered on either side of Ordu Caddesi, discovered during the construction of Beyazit Square in the 1950s. Nevertheless, there's something intangibly momentous about wandering through such a thickly layered cultural metropolis and stumbling upon the main gate into the city ruled by the last sovereign of the Roman Empire. The arch was built adjacent to the Forum of Theodosius, which the emperor modeled on the Forum of Trajan in Rome. The forum, or what's left of it, remains buried several feet below Beyazit Square. It was also called the Forum Tauri, after the colossal bronze bull that greeted visitors at the center of the city.
From the remains, researchers were able to reconstruct (on paper, at least) the monument: The arch was composed of a high center arch flanked by two shorter lateral arches supported by eight sets of four columns topped by Corinthian capitals. Earthquakes and routine sieges on the city reduced much of the forum to rubble well before the arrival of the Ottoman Turks, and many of the buildings constructed later used the site as a marble quarry (some of the columns in the Basilica Cistern originated here, for example).