The sloping terrain necessitated the creation of retaining walls on the north, south and west sides of the plaza. These walls are built of about 24 monoliths at their lowest level each weighing approximately 300 tons.
The Sanctuary of Jupiter Heliopolitanus contains the vast Temple of Jupiter at its western end. The buildings appear to have been planned and begun soon after the foundation of the Roman colony ca. 16 BCE. The oldest building in the complex is the Temple of Jupiter, which was standing almost to capital height by AD 60, as a graffito found on one of the topmost column drums shows. Enlargements and embellishments, including the construction of elaborate approaches to the temple, were carried out down to the 3rd century AD in the time of Philip the Arab, and the architectural decoration of the complex was never entirely completed.