Double Helix Staircase

A freestanding double helix staircase dating from 1499, one of the most significant examples of late Gothic architecture in Europe — two spiral flights wind around the same axis, yet their paths never cross. The stone steps, which have no central column, are supported solely by the mutual pressure of the dressed stone blocks, with no mortar of any kind. The builder remains unknown, and for nearly 200 years the structure was attributed to Leonardo da Vinci owing to its remarkable feat of engineering.