Siena's Italian Gothic Cathedral was mostly built ca. 1215 - 1263. The facade was built from 1285 and into the 14th century.
The Cathedral we see today is actually only one part, the left transept of a much greater church that was planned, but never completed.

Construction on the planned nave was begun in 1339, and one wall was partially completed when the Bubonic Plague
(Black Death) struck the city and took most of Siena's population and wealth with it.
The Cathedral was never completed, but the a single nave wall can be seen in the next image, and testifies to the immense
wealth and ambitions Siena once had.