What is the duomo and who built it?

The Basilica di Santa Maria del Fiore (Saint Mary of the Flower), nicknamed the Duomo after the enormous octagonal dome on its east end, is the cathedral of Florence, Italy, and, arguably, the birthplace of the Renaissance.

A cathedral is a bishop's church. There are many other Catholicchurches in Florence, many of them associated with the Renaissance, including Santa Maria Novella, Santa Croce, and the Brancacci Chapel. However, the Duomo is the home church of the Roman Catholic Archdiocese of Florence, which traces its roots to 394 CE.

Although construction was begun in 1296, the cathedral did not get the structure that gives it its name until 1436. The east end of the church was open to the elements or covered with flat, unstable roofing for more than a century. 

The huge octagonal shape proved daunting to engineers and architects. Italian architects were familiar with circular domed shapes, such as the Pantheon in Rome. However, those domes were constructed with concrete. The recipe for concrete had been lost in the Dark Ages. 

Medieval gothic cathedrals, such as Notre Dame de Paris in France, relied on flying buttresses to support their massive stone weight. Architects and engineers of the budding Renaissance were determined not to use flamboyant Gothic style or flying buttresses—they wanted to look back to the simple, clean lines of their Roman past.

The architect Filippo Brunelleschi came up with a solution. The Duomo is actually two domes. The inner dome is made of sandstone and marble. The outer dome is made of brick-and-mortar—each brick carefully designed, shaped, and fired to support the dome. The dome was constructed without any supports beneath it. 

The Duomo was an immediate success, and Brunelleschi became the chief architect associated with the Renaissance. 

In an ironic twist, the marble facade of the cathedral (not visible in this photograph) was only completed in the late 1800s, during a period when medieval, not Renaissance, art was popular. The birthplace of the Renaissance has a medieval face.

Not quite sure