Alma is referring here to more of his own personal history. As recounted in Alma 9-14, Alma and another man, Amulek, were bound and imprisoned in the city of Ammonihah. The men were saved from incarceration and certain execution when a miraculous earthquake destroyed the walls of the prison, which conveniently fell atop the men’s persecutors, killing them. Alma and Amulek were unhurt.