The walls (1.6km/1mi long) that surround the city were built from 1608 to 1613. The walls contain three main gates, the most famous of which is Ferryquay Gate which the city's apprentices promptly shut against attackers during the siege of 1688-89. To the right of the door, a walk around the fortifications will give you a glimpse of what the city looked like at the time of the siege.