The arch was built between 211 and 214 by means of a testamentary donation of Gaius Cornelius Egrilianus, Prefect of the XIV legion, who was originally from Thebeste. The figure set aside for the construction was 250,000 sesterti.
Later, the arch was reused as the northern gate of the city wall in the Byzantine period. The lateral arches were walled up, as was the northern one, until they were reopened by French military engineers during the colonial period.
In form it is roughly cubical, being 10.94m on the side and to the top of the entablature. On the pylons, beside the spans are pairs of columns with Corinthian capitals, detached from the wall and with pilasters behind, supported by a podium from which their pedestals extend. The main entablature is above the pairs of columns and continues in the recess above the spans. Medallions with the busts of divinities are located above each of the spans.
On the attic on three sides dedications are inscribed to the deified Emperor Septimius Severus, Julia Domna and Caracalla. On the fourth side is a reconstructed Byzantine inscription, originally found in the infill of the vaults, which refers to the incorporation of the arch into the Byzantine city wall as the work of the magister militum Solomon.
At the centre on all sides, the entablature supported an aedicula which held a statue.
The reconstruction of the very top of the arch is the subject of some debate among scholars: According to Meunier an octagonal lantern would have stood there with its base hidden by the aediculae, while according to another there would have been a low dome. According to Bacchielli, the four aediculae, connected by railings contained the statues of the Deified Septimius Severus, the Deified Julia Domna, Caracalla and Geta.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.