Washington proposed a series of frontier fortifications to protect settlers east of the Appalachians. Lewis initially built Fort Dinwiddie on the Jackson River of present-day Bath County, but was relieved of his command September 21, 1755. However, the Virginia assembly soon approved Lewis' promotion to major and assigned him to oversee the region along the Greenbrier River. On February 18, 1756, Lewis led the Big Sandy expedition from Fort Frederick with a mixed force of militiamen and Cherokees to raid the Shawnee towns along the Big Sandy and Ohio rivers to retaliate for Shawnee attacks. Lewis led several expeditions against both Indian settlements and French outposts. During the Forbes Expedition, Lewis was captured during Major James Grant's attack on Fort Duquesne in September 1758. Taken to Quebec, Lewis remained a prisoner until late 1759.