The castle has a tidal dock allowing it to be supplied directly by sea and is surrounded by a water-filled moat. The defences include numerous ingeniously sited arrow slits, and the entrances are protected by murder holes from which substances such as hot sand could be poured over the enemy. Attackers of would have met 14 separate obstacles and four lines of fortification resulting from the 'walls within walls' design.

Some parts of the moat have now been filled in so this part of the wall does not seem as formidible as it once was. Like other concentric castles though, it was virtually impregnable. Beaumaris Castle was positioned to face Garth Celyn on the opposite shore of the Menai Strait and was intended, along with Conwy Castle and Caernarfon castle at either end of the Menai Strait, to overshadow the Welsh Royal home and centre of Welsh resistance.

The dock extends from the south wall and has a further wall (off photo) near the gatehouse so also serves as a defensive firing platform. Unlike the simple outer walls at Caerphilly and Harlech, the walls here are very thick and have internal passages to allow defenders access to protected arrow slits. The foundation that can be seen here is all that remains of the town wall.

All of Edward I's new castles in North Wales were sited where they could be supplied by sea. Ships of up to 40 tons could sail into the dock on the left and unload through the now barred up doorway in the castle wall.

Defenders would be able to rain rocks, arrows, heated sand, boiling oil, water and incendiary devices, and other substances down on the heads of attackers.

This gate through the outer wall is defended by towers and its own two gatehouses. These are not aligned with the inner gatehouses and would have denied attackers the advantage of momentum and a straight path through the gates. The arch on the left is the entrance to the inner bailey.

The outer wall with its 15 towers and arrow loops provided over 300 shooting positions for the archers inside. The massive inner walls create still further levels of firepower. Both walls are well supplied with latrines.

Although never completed it can be seen that the intended accommodation within this inner ward was planned on a lavish scale. Stables, kitchens and private blocks were all planned for as well as an extra story to increase the height of the gatehouse block.

From the highest point within the inner ward there is afforded a good view south across the straight towards the mainland of North Wales.

Unlike many other castles, Beaumaris did not suffer slighting during the Civil War and the castle is very well-preserved. 'Slighting' is the deliberate destruction of a castle without opposition from it's last user. Sometimes this was done by the owners to prevent potential enemies from using the intact fortifications of an abandoned castle. The fortifications of many European cities were slighted in the 19th century because they no longer were effective defense structures and were obstacles to urban expansion.