The Advanced Research Projects Agency Network (ARPANET), the forerunner of the Internet, was a pioneering long-haul network funded by the U.S. Department of Defense’s Advanced Research Projects Agency (ARPA). It served as the test bed for many areas of internetworking technology development and testing, and acted as the central backbone during the development of the Internet. The ARPANET was built using packet-switching computers interconnected by leased lines.