What materials primarily made up Roman concrete?

The combination of lime, sand, and pebbles is significant in the composition of Roman concrete, also known as opus caementicium. This innovative material was crucial for the construction of various monumental structures in ancient Rome, such as the Pantheon and the Colosseum. The use of lime as a binder allowed the concrete to set and harden over time, creating a strong bond that contributed to the durability of Roman buildings. Sand provided additional bulk and stability, while the inclusion of pebbles not only reinforced the structure but also helped in the management of weight and space within architectural designs.

This combination made Roman concrete not only strong but also lighter than traditional stone, allowing for more extensive and complex building designs, such as arches and domes. The added flexibility and adaptability of Roman concrete enabled it to withstand the test of time, contributing to the longevity of many ancient Roman structures that still stand today.