St Paul's Cathedral Dome

The dome of St Paul's Cathedral in London, designed by Sir Christopher Wren, is one of the largest and most influential church domes in the world. It replaced the medieval cathedral destroyed in the Great Fire of London in 1666, whose own tall spire had already been lost to lightning in 1561.

Building the cathedral

Construction of the new cathedral ran from 1675 to 1710. The building was consecrated on 2 December 1697, while work continued. The final stone was placed on the lantern on 26 October 1708, and Parliament declared the cathedral officially complete on 25 December 1711.

A three-part dome

Rather than a single shell, Wren built the dome as three separate structures:

1. An inner dome of brick, seen from inside the cathedral, with an oculus at its apex inspired by the Pantheon.
2. A brick cone, hidden between the two visible domes. It carries the heavy stone lantern, which weighs about 850 tons, and supports the outer dome.
3. An outer dome of timber framing covered in lead, which gives the familiar silhouette over the London skyline.

The inner dome and the cone are each about 457 mm (18 in) thick. Wrought iron chains bind them to stop them spreading and cracking under their own outward thrust.

Height

The dome and lantern rise to about 111 m (365 ft) at the top of the cross.

Survival

The dome survived the Blitz of the Second World War. Bombs struck the cathedral on 10 October 1940 and 17 April 1941; the second is believed to have shifted the dome slightly sideways. Anti-aircraft damage to the dome was repaired by 1967, and a 15-year restoration programme was completed on 15 June 2011.

Significance

The design shows how a lightweight timber-and-lead outer roof can create a monumental external form, while the real structural work is done by a concealed masonry cone. It is a frequently cited example of separating a roof's appearance from its structure.