Aaron was the second oldest of the four sons of Mosiah who went on the mission to the Lamanites, assuming they are listed according to age (see Mosiah 27:34). The city of Jerusalem was located on the east coast by the sea. There is no intent to give a modern geographical location. As mentioned in the Historical Setting, the Amalekites and the Amulonites were apostate Nephites (see Alma 43:13). This explains their bad influence upon the Lamanites.