Egypt has one of the longest histories of any country, tracing its heritage along the Nile Delta back to the 6th–4th millennia BCE. Considered a cradle of civilisation, Ancient Egypt saw some of the earliest developments of writing, agriculture, urbanisation, organised religion and central government. Egypt was an early and important centre of Christianity, later adopting Islam from the seventh century onwards. Cairo became the capital of the Fatimid Caliphate in the tenth century, and of the Mamluk Sultanate in the 13th century. Egypt then became part of the Ottoman Empire in 1517, before its local ruler Muhammad Ali established modern Egypt as an autonomous Khedivate in 1867. The country was then occupied by the British Empire and gained independence in 1922 as a monarchy.