Begun in the later years of Moulay Isma'il's reign, the gate was finished in 1732 by his son Moulay Abdallah.[1][2] The gate's purpose was more ceremonial than defensive, aiming to impress visitors.[21] Its name comes from the architect and designer of the gate, Mansour al-'Alj (the "Victorious Apostate"), a former Christian slave who converted to Islam.[3][8][32] The overall design of the gate is based on Almohad prototypes (such as Bab er-Rouah, Bab Agnaou, etc.), with a large horseshoe-arch opening and flanking bastions, but also presents significant new features. In particular, the flanking square bastions or towers are supported on four thick squat columns at the corners with horseshoe arches between them, creating a hollow loggia at the base of the towers.[21][20] Further out to the sides, flanking the bastions, are massive marble columns supporting large projecting pilasters above. The columns, with ornate composite order capitals, are of ancient Roman origin, probably from nearby Volubilis.[5][33] Almost the entire facade of the gate, including the flanking bastions, is covered in heavy decoration.