Syon Abbey /ˈsaɪən/, also called simply Syon, was a dual monastery of men and women of the Bridgettine Order, although it only ever had abbesses during its existence. It was founded in 1415 and 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, today in the London Borough of Hounslow. 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.).