The Abbey of Santa Maria in Silvis of Sesto al Reghena was founded in 730-735 and belonged from 762 to the Benedictine monks. Despite the fall of the Lombard kingdom in 774 and the rebellion which occurred in the duchy of Friuli in 776 severely repressed by the Franks, the abbey was maintained and ratcheted up its importance even later, because Carlo Magno, in his capacity as King of the Longobards in 781 granted to the abbot blessed a diploma of the confirmation of all properties already accumulated previously and there also added the exemption from any political interference, legal or tax by the secular authorities. In the 899 Hungarians the rovinarono, but the abbey resources in the X century and was fortified. In 967 the emperor Ottone I gave the abbey at Rodoaldo, Patriarch of Aquileia.
In the following years the economic growth of the abbey ensures affluence and floridità the monks and the abbots, so that will be commissioned architectural works, pictorial and sculptural addressed to the best artists working in the area of Veneto-Friuli. Even the fame and the power of the abbot of Sixth grew in proportion, acquiring an always greater prestige in the context of the patriarchate of Aquileia; in 1182 an abbot, Goffredo became patriarch. From 1441 to 1786 the Abbey became commenda; the first Commendatory Abbot was the cardinal Pietro Barbo, who later became Pope with the name of Paul II, and also in the following centuries the title belonged very often a noble Venetian families. In 1818, the religious jurisdiction returned to the Diocese of Concordia and, finally, the title of the abbey was restored in 1921 and assigned to the parish priest pro tempore, belonging to the secular clergy.
In 1431 there were seven defense towers, as represented in the seal of Tommaso de' Savioli, last Abbot residential. Now there remains only one, which also serves as the entrance to the complex; in origin was provided with a drawbridge. The tower was restored by abbots commendatari Giovanni Michiel and Domenico Grimani, who transformed it as today we see; in the eighteenth century it was realized the stone bridge in substitution of the drawbridge. The facade is dominated by a fresco representing a lion of San Marco, dating back to the end of the Fifteenth Century; just below is placed a bas-relief with the coat of arms of Cardinal Grimani with the date of 1521; on the left there is the fresco where is repeated the emblem Grimani, while on the right you find the fresco of a coat of arms with the cross, you ignore the owner. Below you can see painted an allegory of good Venetian government and of the Grimani family, who controlled with its members is the abbey of Sixth that the Patriarchate of Aquileia. Past the tower of entrance leads to the large courtyard, recently paved, on which overlook all the main buildings of the abbey complex.
Just in front of the entrance there is the bell tower, high 33,60 m with square base of 7,70 m and built entirely in brick. It was probably built between the XI and the XII century and is similar to other contemporary towers present in the lagoon area, with vertical pilasters and rare openings along the sides. The face is embellished by high arches a double ring, three per side, of equal height on all sides, except on the southern side, where the central arch was lowered in a second time to place the clock that appears for the first time in a print at the end of the eighteenth century. Beside the bell tower is located a portal of Renaissance origin with a round arch supported by pillars. The whole is made more graceful by pilasters that govern a trabeation with projecting brackets which copies the frame with the teeth of the palace of the abbey.
Under the part absidiale of the Church extends the crypt, restructured between 1907 and 1914, when they were launched major renovation. The crypt is characterized by some small bays, covered by cross vaults, supported by twenty columns, some of which are based on elements of old; while all the capitals are redone. Along the perimeter walls are seats with frames on teeth, in part original. At the center of the crypt is placed the urn of Sant'Anastasia. Consists of a single block of marble of greek origin. The crypt is completed by two lateral apses where above their respective altars are placed a marble Annunciation and a pity.