Hadrian's Wall was built in the 2nd century AD under the Roman Emperor Hadrian to protect Roman Britain from invaders from the north. It extended 73 miles across northern Britain and was constructed by over 7,000 Roman soldiers over 5 years. It featured a stone wall up to 15 feet high with a ditch on either side and 17 forts along it where soldiers were garrisoned. One of the best preserved forts is Housesteads, where 1,000 infantrymen from southern Belgium were stationed. Though its importance declined after Hadrian's death, Hadrian's Wall remains a popular tourist site today that gives visitors a glimpse into Roman Britain.