All along the Tagus estuary are a series of small vauban syle forts defending various landing points, but the most impressive is the Tower of Belem on the old outskirts of Lisbon.
It used to be beyond the shoreline but this is no longer the tidal shore it once was and has been expanded seawards.
The lower level is where the real power lies as it has openning for guns all round. No picture I'm afraid as it was full of tourists.
The level below the guns has ammunition storage and was also used as a prison.
The tower is the forts real feature with a traffic light system for controlling ascent/descent.
Splendid views from the tower across the Tagus.
The other side of the tower with yours truly!