The Butterfly Fort (Pom Phu Sua Somut) is designed in the shape of a butterfly, with the tail serving as the entrance. The western shipping route has since become too shallow for large vessels to navigate, making the fort appear to be closely situated to the Thonburi bank. This fort played a significant role in defending against two French warships that intruded into the Chao Phraya River on July 13, 1893. This event is considered one of the important moments in Thai history.