Bramante had his vision. But he still had to make practical plans for building it. He especially had to figure out how to support the basilica’s huge, heavy dome. Bramante turned again to the ancient Romans. The Romans constructed many buildings, roadways, and other projects. Along the way, they developed concrete. Concrete is a mixture of sand, crushed rocks, and water. Concrete is much lighter than stone or brick. And when it’s wet, it can be poured into shapes. It then dries very hard and strong. The ancient Romans had used concrete to build their domes. Bramante would make the basilica’s dome out of concrete. It would be light enough to be held up by four legs, or piers.
Bramante also planned to use concrete to form the basilica’s ceilings. The ceilings would be rounded, like a series of connected arches. In architecture this is called a vaulted ceiling. Like the dome, the concrete ceiling would be lighter than a stone or brick ceiling. Bramante would not need a lot of walls and columns inside to support the ceiling. That would allow for open spaces inside the church. In the late fall of 1505, Bramante’s workers began digging the foundation behind the old basilica. Once the foundation stones were laid, workers began building the first pier. The four piers would support the dome. They would form the central interior square of the basilica. Each arm of the cross would be built out from a side of that square. Bramante also began to tear down the old basilica. He did not order workers to remove the contents of the church before they began. They destroyed ancient artwork and altars. Angry Romans demanded that they stop. After that, Bramante was careful to tear down the old basilica in sections.