The history of the Internet dates back to the early development of communication networks. In the 1950s and early 1960s, prior to the widespread inter-networking that led to the Internet, most communication networks were limited by their nature to only allow communications between the stations on the network. Some networks had gateways or bridges between them, but these bridges were often limited or built specifically for a single use. One prevalent computer networking method was based on the central mainframe method, simply allowing its terminals to be connected via long leased lines. This method was used in the 1950s by Project RAND to support researchers such as Herbert A. Simon, in Pittsburgh, Pennsylvania, when collaborating across the continent with researchers in Santa Monica, California, on automated theorem proving and artificial intelligence.