Aqueducts were structures used in ancient Rome to transport water from distant sources to cities and towns. They were an essential part of the Roman water supply system, providing water for drinking, bathing, and irrigation. Aqueducts were built with a series of arches and channels to carry water over long distances, often spanning valleys and crossing rivers. They were a remarkable feat of engineering and a testament to the advanced construction techniques of the Roman civilization. The other options, such as the Colosseum, Pantheon, and Trajan's Market, are famous landmarks in Rome, but they are not directly related to the transportation of water like aqueducts.