Caballeros Hospitalarios (Knights Hospitaller) gateway.

It was built in the 13th century by the Knights Hospitaller as an entry point into the city through the city walls.

The gateway is rectangular with a semicircular top. The horseshoe arch entry, is flanked by two towers. There are remains of a Paleochristian sarcophagus from the 4th century that lie in the middle of the blind arches. It has a relief with the cathedral's emblem emblazoned upon it, which represents the placing of San Idelfonso's cassock under the Sun and the Moon which has given the doorway its actual name.