Best viewed from Santichaiprakan Park, Phra Sumen Fort is one of two remaining towers of the historic city wall that once surrounded Rattanakosin Island completely (the other being Mahakan Fort). The historic city wall that followed the Chao Phraya River and Khlong Rop Krung used to have fourteen of these watchtowers, but twelve of them have not endured the test of time. Phra Sumen Fort was constructed in 1783 during the reign of King Rama I to protect the city from potential foreign naval invasions. The fort has an observation tower and two levels of battlements with its original canons still in place.