This temple marks the end of the decumanus and is besides the C3rd area of the city known as 'Diocletian's Camp at the western end of the settlement.
The Tetrapylon that stands today was reconstructed by the DGAM in the 1960s. The original structure was built in the C3rd in the reign of Diocletian. It is a measure of the wealth of the city at this time that the granite columns were imported from Egypt. The structure marks the crossroads where the axis of the main thoroughfare turns to a more acute northern angle.
This basilica is a pre-Christian basilica, probably dating from the C3rd that was later adapted for use as a church. It has also been traditionally linked to the monk who supposedly discussed religion with the Prophet Mohammad in the city.