Ports function as a special area between the land and sea area they connect. Only the player controlling the connected land area may use the connected Port and is considered the Port's "owner".
Port areas may only be occupied by Ship units. Multiple Ship units occupying a Port are considered an army and must be in compliance with supply limits. In addition to normal army restrictions, a Port may never contain more than three Ship units at one time.
If the land area connected to a Port musters new units, the player may muster Ship units directly in the Port itself or in the adjacent sea area.
A player may muster Ship units into a connected Port, even if the connected sea area is occupied by one or more Enemy Ship units. (In fact, the ability to muster ships in a port, even if the connected sea area is occupied by enemy units, is the single most powerful feature of Ports).
Orders in Ports
Just as units in normal areas, Ship units in a Port area must receive an Order token during the Assign Orders step of the Planning Phase. While Defense orders may be placed on a Port, they have no effect as Ports cannot be attacked directly.
Other Port Rules
Ships units may march from an adjacent sea area into a friendly Port, or may march from a Port into an adjacent sea area. However, Ship units may never march into a Port owned by another player.
Ship units in a Port may support a combat in the adjacent sea area but may not support a combat in any adjacent land area (not even in its connected land area). Ship units in a Port provide no defensive Combat Strength to a combat in its connected land area.
Ship units in a Port may raid the adjacent sea area, but may not raid any adjacent land area.
Ship units in a connected sea area may raid a Port. Enemy units in adjacent land areas, however, may not raid a Port.
If, during the Resolve Consolidate Power Orders step of the Action Phase, there are enemy ships in the sea area connected to a port, any Consolidate Power Order assigned to the Port is removed without effect. Otherwise, a Consolidate Power Order in a Port is resolved normally (as if it was in a land area containing no Power icons).
A Special Consolidate Power Order cannot be used to muster units if placed on a port, but may still be used to collect power as normal (subject to the above point).
Taking Control of Enemy Ports
If the land area connected to a Port is successfully attacked and taken control of by another player, that player may immediately replace any enemy Ship units in the Port with an equal number of his own available Ship units (or as many Ship units as he has available, he desires, or is allowed by supply limits). Excess enemy ships are simply removed from the board.
Trade with the Free Cities
When the "Game of Thrones" Westeros card is resolved during the Westeros Phase, in addition to collecting power for each Power icon, players receive one Power token for each friendly Port containing at least one friendly Ship unit, as long as the Port's connected sea area does not contain enemy Ships.