The legion was commanded by a "legate". Aged about thirty, he would usually be a senator on a three year appointment. Immediately subordinate to the legate would be six appointed "military tribunes". Five would be staff officers and the remaining one would be a noble heading for the Senate — originally this tribune commanded the legion. There would also be a group of officers for the medical staff, the engineers, record-keepers, the "praefectus castrorum" (commander of the camp) and other specialists such as priests and musicians.