The Mahmud II Mosque in Constanța, better known by its original name of the Charles Mosque, is one of the main historical monuments of the city by the sea. Built on the initiative and under the patronage of King Charles I, between 1910 and 1913, the Great Mosque of Constanța is a tribute to the city's Muslim community and was inaugurated on May 31, 1913 in the presence of the royal family. In fact, the mosque, the most important edifice of Muslim worship in the country, is known among Muslim believers as the King's Window or Kral Camii.

The monument can be found in Constanța, on Arhiepiscopiei street, at number 5. The Carol Mosque was built under the guidance of the architect Victor Ștefănescu and the engineer Gogu Constantinescu, from stone, brick and reinforced concrete elements, combining the Arab-Egyptian style with elements of specific Romanian architecture . The minaret, built in the Moorish style, is 45 meters high, reaching the top of an internal staircase with 140 spiral steps. As a novelty of the time, the mosque is the first building in Romania where reinforced concrete was used (dome, vaults and minaret). The prayer hall with walls decorated with cult-specific murals houses a huge oriental carpet, over 200 years old, from the island of Ada Kaleh. The famous 126 square meter carpet, weighing 490 kg, had been gifted to the Ada Kaleh Island mosque by Sultan Abdul Hamid (1876-1909).

The Carol Mosque consists of the actual mosque and the inner courtyard with porticoes.