I use the
picture below (place it on top of the unit) to show that a roman unit is
curently in testudo formation. It has the minimal formation depth that
is needed to form a testudo (4 wide, 2 deep). A testudo is declared at
the beginning of the players turn, and gives a 2+ armour save against
missiles, but may not march or charge. Click the picture to get a lager
version.