Borj Nord is a 16th-century fortress built by Saadian Sultan Ahmed al-Mansur to defend the city. It now houses the Arms Museum with a collection of over 8,000 pieces including swords, rifles, armor, and cannons from various eras. Notable is a massive 5-meter cannon used in the Battle of the Three Kings. The hilltop location offers spectacular panoramic views of the old city, rivaling the Marinid Tombs.