Visitors scrape the walls of the former Greek Orthodox cathedral of Hagia Sophia to get small pieces as souvenirs (bottom left). The 6th century world heritage monument, commissioned by Byzantine Emperor Justinian to grace Constantinople (modern-day Istanbul), has suffered plenty of damage since its conversion into a mosque, including to the Imperial Gate (bottom center) and other parts, as well as a broken water tank (bottom right). In view of these incidents, security at Hagia Sophia has been stepped up by Turkish authorities. A total of 70 guards work in shifts inside the building, together with the tourist police, the Turkish newspaper Hurriyet said on Friday. It is estimated that 40,000 people visit Hagia Sophia every day.