Mar Shimun XVIII Rubil (also Simon XVIII Rouel or Rowil) served as the Catholicos-Patriarch of the Assyrian Church of the East from 1861 to 1903, succeeding his uncle Shimun XVII Abraham.^[1]

He led the church from Qodshanis, in southeastern Turkey. In 1869, he received an invitation from the Vatican to attend the First Vatican Council as an observer, but he did not accept the invitation,^[2] and he also rejected other initiatives for the union with the Catholic Church.^[3] The Catholicos-Patriarch died on March 16, 1903, and was succeeded by Shimun XIX Benyamin.

• List of Patriarchs of the Assyrian Church of the East

• Baum, Wilhelm; Winkler, Dietmar W. (2003). The Church of the East: A Concise History. London-New York: Routledge-Curzon. ISBN 9781134430192.
• Baumer, Christoph (2006). The Church of the East: An Illustrated History of Assyrian Christianity. London-New York: Tauris. ISBN 9781845111151.
• Coakley, James F. (1992). The Church of the East and the Church of England: A History of the Archbishop of Canterbury's Assyrian Mission. Oxford: Clarendon Press. ISBN 9780198267447.
• Wilmshurst, David (2000). The Ecclesiastical Organisation of the Church of the East, 1318–1913. Louvain: Peeters Publishers. ISBN 9789042908765.
• Wilmshurst, David (2011). The martyred Church: A History of the Church of the East. London: East & West Publishing Limited. ISBN 9781907318047.

• Official site of the Assyrian Church of the East