Olympia: The Age of Gods PBEM (Oct 4 2000)
Units may issue the behind
command to declare whether they will
be in the front or the rear in battle. Rear units do not become targets
for the enemy until all of the units in the rows in front of them have
been killed. Only missile fighters, such as archers, may attack from
the rear.
Note that rear units do not advance to fill in the front row until a successful attack by the other side. So if a force starts off with all its units in the rear (e.g., BEHIND 9) they will remain in the rear (possibly making missile attacks) until a hit from the other side forces some of them into the front row.
Regardless of whether they are in the front row or behind, nobles will
not receive a hit until all the troops they personally command have been
killed. The leader of each stack (the top-most unit in the stack) will
be the last unit to receive hits, regardless of its behind
status. That is, the leader is effectively "behind" all the other
nobles.
The exception to all these rules are some special attacks, which hit nobles and men alike regardless of where they stand.