Rulebook page 5:
ARES - Move Troops
For 1 GP, the player may move some or all Troops on an isle
to another isle connected by a chain of Fleets of his color.
• If he lands on an isle where enemy Troops are present, a
battle starts immediately.
• If he lands on an isle where there are no Troops, he claims
this isle without a battle, even if the isle has a Fortress.