Syon Abbey , also called simply Syon, was a monastery of the Bridgettine Order founded in 1415 which stood until its demolition in the 16th century on the left (northern) bank of the River Thames within the parish of Isleworth, in the county of Middlesex, on or near the site of the present Georgian mansion of Syon House. It was named after the Biblical Holy City of David which is Zion (1 Kings 8:1), built on the eponymous Mount Zion (or Sion, Syon, etc.).