The ancient city was once encircled by high wall, protected by 16 fortresses. Among the most important of these was the Pom Phet ("Diamond Fort") which sits at the southern tip of the island at the confluence of the Chaophraya and Pasak Rivers.

The fort was rebuilt several times over the centuries. The last reworking was probably done by the French in the late seventeenth century. The walls and forts didn't stop the Burmese, and much of the walls and forts were dismantled to be reused in the construction of the new capital at Bangkok.

Much of what can be seen today is a reconstruction, now set in a nice park that's a pleasant place to relax in the late afternoon.