Arches are curved structures designed to support or strengthen a building. Although the Romans did not invent arches (they had been used since prehistoric times), they were the first ones to design arches that could support enormous amounts of weight.
This was achieved thanks to the development of concrete, which was a mixture of lime and volcanic sand. Creating structures out of concrete meant the weight of the building could be supported through structures like arches, without the need of pillars or columns. This innovation allowed them to achieve structures that had never been used in architecture before. For example, the combination of arches gave rise to vaults, and the same principles were applied to develop domes. The developments spread all over the world, allowing architects to develop larger and more complex buildings.
