Lewes was the county town of Sussex before the county was divided in 1974, and is now the county town of East Sussex. It stands on the River Ouse, 6 miles NE of Brighton. The ruins of the priory are in Southover, on the SE edge of the town and the former hospitium of the priory, at the W end of the precinct, was turned into the parish church of St John the Baptist in the 13thc. The original arrangement had two parts of unequal widths, separated by an arcade, perhaps to divide the sexes. The wider N section became the nave and the S section the aisle. The nave was apparently curtailed for the building of a W tower at an unknown date (although the tower arch appears to be 14thc work). The nave is now 5 bays long on the N wall with a 4 bay S aisle. The original tower collapsed in 1698 and its replacement, of brick, dates from the 18thc. The chancel is of 2 bays, of the 15thc extended in the 19thc. At the E end of the S nave aisle is the chapel of William of Warenne and Gundrada, added in 1845 by J. L. Parsons of Lewes under the guidance of Benjamin Ferrey. It contains two lead coffins discovered during the excavations of 1845-47 carried out when the railway line to Brighton was built across the priory site. They contained bones assumed to be those of the founders, which were interred beneath the beautifully carved Tournai marble slab to Gundrada (d.1085) that had been brought from Isfield church in 1775. Romanesque work recorded here consists of part of the nave arcade, Gundrada's tomb slab and the plain font.

The church was originally the hospitium at the gate of the Priory of St. Pancras, which was converted into a parish church in the 13thc when, possibly, the new Hospital of St. James was built close by.

The older literature makes Gundrada (d.1085) a daughter of William the Conqueror, but this is no longer accepted by modern historians who believe she was of Flemish origin. The arrangement of inscriptions on her tomb slab, however, bears strong similarities to that of Matilda, William's queen, in the Abbaye aux Dames at Caen. There is no record of an earlier memorial before the pair were reburied in the new chapter house, probably in the 1160s. Their tombs wer removed at the Dissolution, and in 1775 Dr Clarke, Rector of Buxted, discovered Gundrada's tomb which had been re-used on the table tomb of Edward Shirley in Isfield church. The trimming of the slab was apparently to makem it fit the Shirley tomb. William Burrell paid for its removal to St John's, Southover, and it was placed in the rectory pew until the present chapel was built for it in 1845-47.

Frieda Anderson commented on the Gundrada tombslab as follows: The Gundrada tombslab is the finest surviving Tournai marble tombslab in Europe. English and Flemish characteristics are intermingled. Motifs from the Winchester and Lambeth Bibles are apparent, while the nearest equivalent of the palmettes may be seen in Flemish manuscripts, especially those from the Abbey of Marchiennes. Technically the skill of the sculptor, his ability to undercut the hard material, and his use of hatching, suggest a Flemish sculptore. On the other hand, the employment of motifs found on other pieces from the Priory workshop, especially nailhead and multi-stranded banding, makes it likely that the slab was carved in Lewes. A visiting Flemish craftsman or atelier resident at Lewes seems the most likely possibility. An atelier of Lewes Priory craftsmen visiting a great Flemish Abbey, like St Bavon, Ghent, cannot be ruled out.

Zarnecki (1984) remarked on the striking similarity between this and the capitals from the cloister of Glastonbury, carved in Blue Lias, a similarly hard and fine-grained stone. The Glastonbury cloister was built under Abbot Henry of Blois, who also imported the Tounai font to Winchester cathedral, was trained at Cluny, the mother house of Lewes. Hie concluded that the tombslab was carved by an English sculptor in Henry's service, who subsequently worked at Glastonbury, and offered a date of c.1145 for Gundrada's tombslab.

The font is enigmatic. Nairn (1968) made no mention of it, while for Antram (2012) it looks C19, yet it has the marks of staples, indicating a medieval date. It is also illustrated, rather surprisingly for such a plain font, in Paley (1844) where it is described as a 'massive square Norman bowl'.