St Paul's Cathedral familiar with the unique octagonal lantern tower over the crossing of Ely Cathedral, which spans the aisles as well as the central nave, unlike the central towers and domes of most churches. Wren adapted this characteristic in designing the dome of St Paul's. In section St Paul's also maintains a medieval form, having the aisles much lower than the nave, and a defined clerestory. The most notable exterior feature is the dome, which rises to the cross at its summit, and dominates views of the City. The height of 365 feet is explained by Wren's interest in astronomy. Until the
Butter-churn tower was 54 metres high at the intermediate platform, but was destroyed in 1797. The third-highest surviving bergfried in Germany is at the Osterburg near Weida in Thuringia; it is 53 metres high and also designed as a butter-churn tower. It is also one of the oldest surviving bergfrieds, dating to 1193. It measures 24 metres to the platform and has an octagonal, stone conical roof dating to the 15th century. Butter-churn tower A butter-churn tower () is a two-part defensive tower in which the upper section has a smaller diameter than the lower section. This design provides a ledge or