Situated on the Cardus Maximus of the Roman street-grid it took its name, in the XV century, from a nearby sarcophagus lid bearing two lions and which is now situated behind Umberto I monument.
The gate was thirteen meters high (as high as the city walls), had a square plant and an internal courtyard, two fornixes on the façades and tunnel-vaults on the upper levels.
Two plygonal towers connecting the walls flanked the external façade and numerous windows looked onto the towers and the passage ways.