The whole of Lewes Priory monastic site of about 16 hectares (39 acres) was surrounded by a wall and the main entrance was on the north side of the site. The map of Lewes circa 1775 by William Figg shows a gateway at the east end of Southover Church, at right angles to Southover High Street, and opposite the junction of St James Street and the entrance to St James's Hospital. It makes sense that the entry was on the town side and on the line of the former Antioch Street (which joined the main road of Lewes between St Anne’s Hill and Westgate).
The drawing prepared by Harold Brakspear following the 1904 excavations shows a more detailed conjectural layout of the gateway. Part of it is reproduced here by kind permission of Sussex Archaeological Society.
The structure would have been impressive with battlements and rooms above a central vaulted entrance flanked by a side gate. It is not clear why the gate faced west along Southover High Street rather than north towards the town. Making visitors turn through two right angles to enter the main open space at the west end of the great Priory Church may have been for defensive reasons or for privacy. There are several drawings of this gateway between 1772 and 1832 which are reproduced below. They show the remains of a wide opening (for horses and carts) with a narrower pedestrian one on its left. In the earlier prints the Priory grounds can be seen beyond and in the later the openings have been blocked up.
Southover High Street was widened, presumably after the Henwood engraving of 1832. This required the removal of at least part of the gateway structure. The work may have been associated with the building of Priory Crescent which started in 1836. All we know for certain is that the side gate was relocated at the west end of the Crescent which was the last part to be completed in 1852.
Gateway and Walls to Priory of St Pancras, Lewes are included on the Statutory List of Buildings of Special Architectural or Historic Interest Grade II.
British History Online has this to say about the Priory Gateway:
"Close to the east wall of Southover parish church are the remains of the Great Gate of the priory. It was a square building with two adjacent archways in its west wall and a stair-turret at the north-west angle. The southern arch was approximately 10 ft. wide and the northern 5 ft. The south jamb of the former arch survives, and shows that it was of four orders, each with a shaft, moulded base, and capitals. The material is Sussex marble; the free shafts have disappeared, but the capitals, bonded into the masonry, show square abaci and stiff-leaf foliage, and the hollow mouldings have carved leaf ornament. The smaller archway has been re-erected at the west end of Priory Crescent and now shows a two-centred pointed archway. An 18th-century drawing by Lambert represents it as semicircular and the span of the arch has been evidently reduced. The date of the gatehouse, which must have been a building of great importance and beauty, is about 1200. Portions of its southern wall still exist, bounding the parish churchyard, and there is part of an archway in this wall at right-angles to the entrance."