Samut Prakan was built as a frontier town to protect the approach to Bangkok upriver. Fortresses were built on both sides of the river from the estuary all the way up to Phra Pradaeng. Not many of these forts are around today. They are either in ruins or the bricks have been removed for construction projects in Bangkok. The most famous fort, which is still in good working order, is probably Phra Chulachomklao Fortress which has been open to the public for a number of years. Now there are plans to open another fort to the public.

This is Phi Sua Samut Fortress which is unique as it is on an island in the Chao Phraya River. It is situated in Samut Prakan between the City Hall and Phra Samut Chedi. It was built at the same time as Phra Chulachomklao Fortress in the 1880's. During that time, colonial powers such as France and Britain were flexing their muscles and taking over territory in the region. King Rama V saw a need to renovate and build new fortresses along the Chao Phraya River. The two main forts were built at the entrance to the estuary and on an island near Phra Samut Chedi.

King Rama V ordered at great expense the latest guns from W G Armstrong & Co in England. These were ten 6 inch Armstrong Guns which weighed five tons each. They were the first rear-loaded guns in the Thai Navy and they had an interesting characteristic. They were called the "disappearing" guns because they only came out of the pit to fire and then the recoil forced the gun back where it came from. This protected the guns from enemy fire. All of the aiming had to be done while the gun was in the pit. Each shell weighed 45 kilos. The gun was then hauled up be a hydraulic mechanism and the shot fired. The range was about 8 kilometres.

Seven of these guns were installed at the Phra Chulachomklao Fort. The remaining three were set up at Phi Sua Samut Fort. About three months after their completion they saw action for the first and only time. On 13th July 1893, two French gunboats entered the estuary with the intention to blockade Bangkok. Shots were fired and a small boat that was acting as a pilot for the French ships was badly damaged and ran aground. Despite heroic action by the soldiers at the fort and the sailors aboard ships on the river, the two French gunboats managed to slip by. By the time it reached the inner fort it was too dark for anyone to continue the battle. The gunboats were then able to go all the way up the river to Bangkok.

As Phi Sua Samut Fort was on an island, it managed to survive the years in relative good condition. The land is owned by the Royal Thai Navy and there was restricted access. For the last few years, engineers in the navy have been busy renovating the Armstrong guns. They have also built a boardwalk through the mangroves. On the island there are several thousand fruit bats that come out to hunt at dusk. Once it is opened to the public, it will be an interesting place to visit which combines both nature and history.

To make it easier for tourists to visit, the local administration have proposed the building of a bridge between the pier at Phra Samut Chedi and the northern end of the island. The proposed budget is 25 million baht which hasn't been approved yet. There is no indication yet how long this will take to build once approved. In theory, it is possible to visit the island now. Get on the ferry boat at the pier at Phra Samut Chedi. You will need to ask the captain to drop you off at the island which is only a short distance away. They will only stop for a few seconds so be prepared to jump. To go back, you need to flag down a boat heading to Paknam. Make sure you leave the island before low tide otherwise you will be stranded.