The ruins of Croyland Abbey are of exceptional interest and show many styles of architecture. The west arch of the central tower with its zig-zag moulding is Norman work, and is undoubtedly the most ancient part of the ruin. The west front consists of two styles--Early English in the lower part and Perpendicular in the upper. The north-west tower was erected in 1427; its buttresses and spire, and also the adjoining west porch are, however, 16th century work. The remainder of the ruins are mostly Perpendicular--the nave, aisle, transepts and Lady chapel having been built in the 15th century. The north aisle of the abbey church has been used as the parish church since 1688 when the roof of the abbey fell in. Croyland in its prosperity was one of the most wealthy and magnificent monastic foundations in England. Founded in Saxon times, it was re-established after the Norman invasion and subsequently became a mitred abbey. The original church and monastery suffered greatly at the hands of the Danes in the 9th century, the “Abbot being slain at the altar where he was celebrating the Holy Communion and many of the monks being tortured and killed in the most cruel manner.” Shrines and monuments were specially singled out by the Danes for destruction, the sacred contents being irreverently scattered in all directions, and the costly memorials rifled. But for the influence of monasticism, Croyland (derived from the Latin _Crudam terram_--muddy land) might still be a small and insignificant island. Owing to the religious enterprise and enthusiasm of King Ethelbald, the abbey was built on the tract of land with which he endowed it. At his instigation oak and alders were driven in as piles, and hard earth brought in boats from the upland. An excellent system of drainage, too, was carried out, converting marsh into rich pasture land, watered by the Welland alone instead of the four streams by which it was originally enclosed.