Question

Who designed these domes and which has the longest clear span?

Hagia Sophia Florence Cathedral Saint Peters in Rome St. Paul’s Cathedral in London American Pavilion in the 1967 World’s Fair in Montreal

Answer

Hagia Sophia: Anthemius of Tralles and Isidore of Miletus
Florence Cathedral: Filippo Brunelleschi
Saint Peters in Rome: Michelangelo
St. Paul’s Cathedral in London: Sir Christopher Wren
American Pavilion in the 1967 World’s Fair in Montreal: Buckminster Fuller

Fuller's geodesic dome (now destroyed) at over 300 feet (90 meters) was, in its day, the largest clear-span structure in the world.