Citadel of Acre The current building which constitutes the citadel of Acre is an Ottoman fortification, built on the foundation of the Hospitallerian citadel. The citadel was part of the city's defensive formation, reinforcing the northern wall. During the 20th century the citadel was used mainly as a prison and as the site for a gallows. During the British mandate period, activists of Jewish Zionist resistance movements were held prisoner there; some were Knights' Halls Under the citadel and prison of Acre, archaeological excavations revealed a complex of halls, which was built and used by the Hospitallers Knights. This complex was a part of the Hospitallers' citadel, which was combined in the northern wall of Acre. The complex includes six semi-joined halls, one recently excavated large hall, a dungeon, a dining room and remains of an ancient Gothic church. Medieval European remains include the Church of Saint George and adjacent houses at the Genovese Square (called Kikar ha-Genovezim or Kikar Genoa in Hebrew). There were also residential quarters and marketplaces run by merchants from Pisa and Amalfi in Crusader and medieval Acre. Conservation projects Acre's Old City has been designated by UNESCO as a World Heritage Site. Since the 1990s, large-scale archeological excavations have been undertaken and efforts are being made to preserve ancient sites. In 2009, renovations were planned for Khan al-Omadan, the Inn of the Columns", the largest of several Ottoman inns still standing in Acre. It was built near the port at the end of the 18th century by Ahmed Pasha al-Jazzar. Merchants who arrived at the port would unload their wares on the first floor and sleep in lodgings on the second floor. In 1906, a clocktower was added over the main entrance marking the 25th anniversary of the reign of the Turkish sultan, Abdul Hamid II.