Syon Abbey / ˈ s aɪ ə n /, 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 …