Custodian of the Two Holy Mosques (abbreviation CTHM; Arabic: خَادِمُ ٱلْحَرَمَيْنِ ٱلشَّرِيفَيْنِ‎, Khādim al-Ḥaramayn aš-Šarīfayn), Servant of the Two Noble Sanctuaries or Protector of the Two Holy Cities, is a royal style that has been used by many Muslim rulers, including the Ayyubids, the Mamluk Sultans of Egypt, the Ottoman Sultans, Kings of Hejaz and in the modern age, Saudi Arabian kings. The title was sometimes regarded to denote the de facto Caliph of Islam, but it mainly refers to the ruler taking the responsibility of guarding and maintaining the two holiest mosques in Islam: Al-Haram Mosque (Arabic: اَلْمَسْجِدُ ٱلْحَرَامُ‎, romanized: Al-Masjid al-Ḥarām, "The Sacred Mosque") in Mecca and the Prophet's Mosque (Arabic: اَلْمَسْجِدُ ٱلنَّبَوِيُّ‎, romanized: Al-Masjid an-Nabawī)