

On 5 November 1938, Balbo inaugurated an equestrian statue of Benito Mussolini in front of the castle. In the 1930s, governor Italo Balbo established his office inside the building. Brasini's initial plan was to have even more arches built, including a second level above the ones that were constructed.

Brasini modified the Saint George Bastion to a more medieval appearance, created a new (albeit ancient-looking) entrance portal, and built the castle's iconic arches above the eastern (Saint James) bastion, originally facing the sea and now on the Saraya Lake. In 1922-23 it was correspondingly refurbished along designs by architect Armando Brasini, who took a creative approach to its renovation. In 1919 it was converted into a museum, the first in Libya's history. Īfter the Italian conquest of Libya in 1911, the castle was initially used as residence for the Italian governor-general. As such, the castle was the center of power under Ahmed Karamanli and the Karamanli dynasty (1711-1835). The first Ottoman governor or Pasha of Tripoli, Murād Agha, converted the castle's Church of Saint Leonard : 388 into a mosque, and subsequent governors made the building into their residence. The castle is also said to have been painted red ochre during that time, thus its current name. Much of the current structures appear to date from the subsequent period of rule by Aragonese military commanders and, after 1530, by the Knights Hospitaller until their expulsion by the Ottoman Empire following the Siege of Tripoli (1551). In 1510 Tripoli was conquered by the Kingdom of Aragon. Like the surrounded region, it was taken over by the Vandal Kingdom around 439, recovered by the Roman Empire in 534, overrun by Amr ibn al-As in 642 or 643, reconquered by the Byzantines then again by the Umayyad Caliphate in the late 7th century then under the rule of the Abbasid Caliphates (750-800), the Aghlabid Emirate of Ifriqiya (800-909), the Fatimid Caliphate (10th century) who refurbished it into a royal residence, the Zirid Emirate of Ifriqiya and Banu Khazrun (11th century-1146), the Norman Kingdom of Africa (1146-58), : 383 the Almohad Caliphate (1158-1229), the Hafsid Emirate of Ifriqiya (1234-1321), the Beni Ammar (1321-1401) and again the Hafsid Emirate (1401-1510, with another lapse in the mid-15th century).

The origins of the castle may be as old as the Phoenician foundation of Oea in the 7th century BCE excavations have found remains dating back to Roman times. Early 16th-century map of Tripoli by Piri Reis, indicating the Red Castle on the left
