At the head of the nave is the internal dome, supported by ionic columns and buttressed by external walls. It rises to a height of 21.33 meters (70 feet) from the floor. The internal dome is one of the basilica’s main artistic features, and over this dome rests the coppered cupola (the external dome). The cupola rises to a height of 35 meters (115 feet) and is 12.19 meters (40 feet) in diameter at the base.
The interior of the external dome was re-timbered at the time of the Silver Jubilee in 1936, as “sufficient care was not taken during the building”. The copper for the dome cost £600.