The Mosque of Cristo de la Luz is the only of the ten former mosques of Toledo which remains largely as it was in the Moorish period. It was then known as Mezquita Bab-al-Mardum, deriving its name from the city gate Bab al-Mardum. It is located near the Puerta del Sol, in an area of the city once called Medina where wealthy Muslims used to live.

The mosque is a small building, measuring about 8 x 8 m. Four columns capped with Visigothic capitals divide the interior into nine compartments. Above these are nine vaults, each with a distinctive design. Behind this square section, a Mudéjar semi-circular apse contains frescoes of Pantocrator and the Tetramorphs.

An inscription written with brick in Kufic script on the south-west facade reveals the details of the mosque's foundation: Bismala (in the name of Allah). Ahmad ibn Hadidi had this mosque erected using his own money requesting a reward in paradise for it from Allah. It was completed with the aid of Allah under the direction of Musa ibn Alí, architect and Sa'ada, and concluded in Muharraq in the year 390 . According to legend, when King Alfonso VI entered Toledo in conquest in 1085, his horse knelt before the door of the mosque. A shaft of light guided the king to a figurine of the crucified Christ which had been hidden for centuries. He left his shield there with the inscription, "This is the shield which the King Alfonso VI left in this chapel when he conquered Toledo, and the first mass was held here". In 1186, Alfonso VIII gave the building to the Knights of the Order of St John, who established it as the Chapel of the Holy Cross ( Ermita de la Santa Cruz). They extended it by adding the apse.