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
Mather Tower footprint. This resulted in a multitude of tall, slender, "setback" towers, of which the Mather is an extreme and unusual example. The top floor of the octagonal spire has only of floor space. Mather Company's founder, Alonzo Mather (a descendent of Cotton Mather) is said to be responsible for a number of the building's distinctive design features, including the octagonal tower. Initial plans called for construction of a second, identical building on North Michigan Avenue, behind the Mather and connected to it by a ground-floor arcade, but onset of the Great Depression in 1929 forced its cancellation. By the 1990s