Fort "Peter I" or "Citadel" is a historical and architectural monument of the 18th century. It was created to protect the Merchant Harbor from the south. It is under state protection. It is located near Kronstadt. Peter I, understanding that one Kronshlot was not enough to defend Kronstadt and Saint Petersburg from the Swedes, arrived at Kotlin in May 1705 to place a coastal battery on the island. The construction was overseen by Kruys, and the battery was named after Saint John.

By the time the Swedes appeared on the island, there were already five batteries reinforced with naval guns. The batteries performed well in battles, but in a letter to Peter, Kruys, assessing their actions, gave a recommendation for improvement: "it would not be bad to build another fortress for Kronshlot or near it." As a result, in 1706 the fortress "Saint Alexander" was built on the site of the Tolbukhin battery, and the Saint John battery was strengthened, which was still insufficient. However, the hostilities of the Northern War shifted southward, and Peter temporarily turned his attention away from Kronstadt. During this time, only infrastructure objects were built: piers, barracks, houses, shops, etc. Peter returned to the problem of defending Kronstadt and Saint Petersburg only after the signing of the Treaty of Nystad.

In 1721, Peter demanded protection for the ships located in the Merchant Harbor from sea bombardments. First, the Saint John battery was reinforced, and then, realizing the insufficiency of this measure, a new battery—the "Citadel"—was built. Unlike its predecessor, the Kronshlot fort, the Citadel featured more powerful bastions and armament. Thanks to the creation of the fort and the ability to conduct crossfire together with the Kronshlot fort, the defense of the Kotlin roadstead, through which enemy ships could break through to Saint Petersburg, was significantly strengthened.

The construction was led by Captain Lane, carried out by soldiers and officers of the Semenovsky and Preobrazhensky regiments. The fort was built on piles and, like Kronshlot, has an inner harbor. Upon completion in 1724, the battery had 106 guns and powder magazines on piles. Later, for safety reasons, the powder was moved into the parapets.

After that and until the flood of 1824, the fort was only slightly repaired.

In 1824, Saint Petersburg and Kronstadt were subjected to a devastating flood. Most of Kronstadt's fortifications were destroyed or seriously damaged; about two thousand guns were torn from their places, damaged, and carried out to sea. The wooden fort did not escape this fate either.

Compared to the old fortress, new piles and a concrete foundation were added, which significantly strengthened the fort. The masonry of the towers was made of rubble stone and faced with granite on the bay side. The joints were sealed, and the wall thickness was increased to 2 meters.

After reconstruction, the fort's defense was carried out on a circular principle. The main tower was connected on the flanks with two half-towers. The gorge part, with two passages to the fort's inner harbor, was armed with sixteen half-pood unicorn guns, and the passages themselves were covered by cast-iron sliding bridges. The fort housed a garrison of 422 people armed with 97 guns. Upon completion of construction on September 7, 1834, by decree of Nicholas I, the fort was named Peter I.

Due to the threat posed by the English fleet during the Crimean War, in 1854 the first underwater mine barrier in the world was installed between the forts "Alexander I" and "Peter I," and shortly after—between the forts "Kronshlot" and "Peter I." The length of the mine position, equipped with Jacob mines, was 555 meters.

Subsequently, the fort was moved to the second line of defense, then used as a transshipment base—in 1870, a dam, bridge, and pier with a revolving crane were added to it. And in 1896, due to the increased range of artillery, which made it possible to shell Kronstadt from the mainland shore, the fort was completely removed from the defensive structures. Despite this, during the transformation of Fort "Alexander" into an anti-plague laboratory, "Peter" received all its armament. At different times, it housed chemical laboratories for the production of explosives and storage sites for ammunition. During the Great Patriotic War, mines, shells, and torpedoes were prepared here around the clock. During the first week of hostilities in 1941, 3,300 mines were laid, which destroyed 17 German and 3 Finnish ships. After the war, the laboratory at the fort was closed; until the beginning of the 21st century, the fort housed various storages and a workshop for repairing naval shells.

Fort "Emperor Peter I" is a historical and architectural monument of the 17th–20th centuries and is included in the UNESCO World Heritage List. Its appearance preserves a fascinating history related to the development of fortification art in Russia, the Kronstadt fortress, mine-torpedo armament, and the "gunpowder military craft."

Sources:

https://xn--80aiqmelqc4c.xn--p1ai/press/news/fort-citadel-postroen-po-staroj-derevozemlyanoj-tehnologii1/

https://ru.wikipedia.org/wiki/%D0%9F%D1%91%D1%82%D1%80_I_(%D1%84%D0%BE%D1%80%D1%82)