The main function of the ARPANET in the history of the internet was to serve as the precursor to modern networking. Developed in the 1960s, it was initially a project funded by the U.S. Department of Defense to ensure reliable communication among various research institutions. ARPANET introduced key protocols like TCP/IP, which became foundational for the internet's architecture. By connecting computers and facilitating data exchange, ARPANET demonstrated the feasibility of decentralized networks, paving the way for the global internet we use today. Its legacy reflects the critical early steps in network exploration and development.