So the Etruscan infantry 1st,2nd and 3rd class may combine in a TUG 3 rank deep at the deployment. ( special rule )
Minimum is 16 bases ( 8 + 8 )
Nw to be perfectly clear the 3 rank mandatory "deployment" may be ignored later during movement and melee so second and/or 3rd rank can deploy and enlarge the TUGs front, the 3 rank deep formation being mandatory only at deployment . not during movements, charges, pursuit and end of contact with the enemy . Correct ?
Because the TuG size is 6,9 - the minimum is actually 18 bases.
The restriction is at deployment. After deployment you can expand the formation or shift the ranks around as you wish. Note however that the pilum only ever shoot from the front rank.
Richard