The Greek Orthodox Church of Jerusalem ( "Kanisatt Ar-rum al-Urtudoks fi al-Quds", literally Rûmi Orthodox Church of Jerusalem; ), officially called simply the Patriarchate of Jerusalem (, "Patriarcheîon Hierosolýmōn"), is an autocephalous church within the wider communion of the Eastern Orthodox Christianity. It is headed by the Greek Orthodox Patriarch of Jerusalem, the incumbent being Theophilos III since 2005. Christians believe that it was in Jerusalem that the Church was established on the day of Pentecost with the descent of the Holy Spirit on the disciples of Jesus Christ () and that the Gospel of Christ spread from Jerusalem. The church celebrates its liturgy in the Byzantine Rite, whose original language is Koine Greek, the original language of the New Testament, and follows its own calendar of feasts, preserving the Julian calendar (that is thirteen days behind the Western (Gregorian) calendar). It is also often called "Σιωνίτις Εκκλησία" (, i.e. the "Church of Zion").