The Mausoleum and Bastion Wall with Gates and Railings

The mausoleum and surrounding bastion wall with gates and railings were designed between 1726 and 1729 and built between 1729 and 1742, with later additions and supervised primarily by William Etty, Clerk of Works, and Daniel Garrett. The design by Nicholas Hawksmoor was inspired by the Tomb of Metella. Interior carvings were undertaken by Charles Mitley.

The mausoleum is a circular, peripteral mortuary chapel built on a square plinth, containing a burial crypt, and encircled by a square bastion wall. Its construction is in sandstone ashlar, topped with a lead roof, and features wrought-iron gates and railings. The north-east facade has an entrance to the crypt, with an ornamental iron gate beneath a lintel and flanked by broad ashlar pilasters and two flights of steps with a damaged column-on-vase balustrade, which leads up to the piano nobile. A moulded plinth carries a 20-column Doric peristyle and entablature. The cella's entrance has a six-fielded-panel door within a moulded architrave with a pulvinated frieze, beneath a canopy supported by moulded corbels. Similar blind entrances are on each quarter, separated by niches with a continuous moulded impost band. The first floor has a moulded band, above which are round-headed, 35-pane unequal sash windows with radial glazing, in pilastered architraves with keyed hoods, also divided by niches mirroring those below. Blind square openings are positioned in moulded architraves above. Eight 20-pane sashes are set within eared architraves, separated by lead downpipes and above a moulded cornice and blocking course, culminating in a domed roof. The bastion wall features squared rusticated projections with a Greek key frieze at the angles and in pairs on each facade; it is separated by ashlar semicircular projections and rusticated broad pilasters with Greek key friezes. Scroll-decorated, semicircular gates are centrally positioned on the north-east facade, flanked by lancet railings that surmount the wall and the first pilaster on either side.

The vaulted crypt holds 63 catacombs. The cella features Corinthian columns recessed into the walls, set on high plinths, carrying a rich entablature and a coffered ceiling. Horace Walpole famously described the mausoleum as a building that "would tempt one to be buried alive".