The altar at Gilgal, constructed by Joshua after crossing the Jordan River (Joshua 4-5), served primarily as:

A A permanent temple for sacrifices throughout the period of the Judges. B A symbolic memorial to God's faithfulness in fulfilling his promise to bring Israel into the Promised Land, and a reminder of their covenant with Him. C A military outpost to defend against attacks from the Canaanites. D A burial site for the Israelites who died during the crossing of the Jordan.