The Abbey of Santa Maria in Sylvis (Italian: Abbazia di Santa Maria in Silvis) is a monastery in the centre of Sesto al Reghena, in the province of Pordenone, north-eastern Italy.
The abbey, founded around 730–735 AD, belonged to the Benedictines until 762. After the fall of the Lombard Kingdom in 774 and the subsequent rebellion of Friuli in 776, the abbey had all its properties confirmed by Charlemagne through a chart including total exemption from any tax obligation to lay authorities.
In 899 it was ravaged by a Magyar raid, and was restored in the 10th century, including the addition of fortifications. In 967 emperor Otto I donated it to Rodoald, patriarch of Aquileia. In the following years the abbey prospered, commissioning numerous paintings, sculptures and architectural additions to Venetian-Friulian artists. One of its abbot, Godfrey, was elected patriarch of Aquileia in 1182.
From 1441 to 1786, the abbey was a commandry; its first lay abbot was cardinal Pietro Barbo, later Pope Paul II; in the following centuries he was succeeded in general by members of noble families from the Republic of Venice. In 1818 it returned to the diocese of Concordia and in 1921 it was restored as an abbey.
Although some form of fortification existed from the abbey's very beginnings, a true line of walls was added in the 10th century after the Magyar assault. In 1431 it had up to seven towers, only one of which remains today; this was restored to the current Renaissance appearance by lay abbots Giovanni Michiel and Domenico Grimani (late 15th–early 16th centuries), while in the 18th century a stone bridge replaced the previous drawbridge.