The northern, longer part of the fortress is what’s called a “hornverk”. It’s made out of two parallel mounds that ends and finishes with half a bastion and a short wall that separates them, a curtain wall. This gives extra enforcement of the fortress’s northern wall. It’s important to not leave any area bare, as that would make it easier for the enemy to move forward on the island.

On multiple spots inside the hornverk are short adjacent walls. These are called buttresses and help support the sides of the main wall. The space between the buttresses were previously filled with dirt to increase the stability further. On top of the buttresses, decks were built for lining up cannons. In the soil, traces of past structures have been found, for example a larger barrack north of the hospital and a storage building west of the bridge leading to the southern part of the island. In front of the curtain walls of the hornverk a smaller moat was built and named Smedjebatteriet. Out of all the houses and buildings built inside the hornverk, only the hospital remains today.