A "line" in CCA is any group of units that each have another unit in at least one of its adjacent hexes therefore the "Line" does NOT have to a straight line in the true sense of the word.
A group forming a triangle or a diamond (square) would qualify as a line for the purposes of this card. Think of it like the "Inspired leadership" cards.
As long as the units to be ordered are ALL foot units (no mounted including a leader on its own in a hex)then the possible arrangements are endless - in arrangement and number!
