The town walls date from the 13th century and, with later additions and renovations, stretch from the fortress down to the square where they join the third wall in an east–west direction. This wall is practically camouflaged by a series of patrician houses built into it. The walls are interspersed with four-cornered side towers, the construction of which lasted, with essential repairs, from the 13th to the 16th century. The current fortress Fortica, also known as Tvrđava Španjola ("Spanish Fort") was constructed following the gunpowder explosion in 1579 which devastated the old fortress. Today, the fortress includes a modern tourist complex, and provides a superb view of the town and its surroundings. In 1811, during the rule of the Napoleonic Empire, a second fortress Trđava Napoleon was constructed on the higher hill to the northeast. The site now also houses an observatory.