The fortress was built on a giant hill so the guards could see intruders coming from miles away - by land or sea. Enemies that attacked by water came through the bay because they were less likely to hit sand bars. Cartagena's first line of defense was a giant underwater chain that stretched from one side of the canal to the other. When they spotted an enemy ship approaching, they lifted the chain so the ships could not pass.
When enemies attacked by land, they had to get by the fortress first. The fortress is massive - wide at the bottom and full of dark tunnels. There are many secret tunnels that soldiers used to escape from the fortress if necessary. Some tunnels led to a dead end in order to confuse & capture the enemies. Each tunnel has small inlets off the side where soldiers could hide if the enemy was able to get past the canons & through the giant wall. The inlets were staggered so if the soldier attacked the enemy, they wouldn't hurt their fellow soldiers across the tunnel.
It was a very impressive structure and we recommend visiting if you are ever in Cartagena!
Question for Mrs. Barbier's class 2A: Who were the earliest enemies to attack colonial Cartagena? Hint: They traveled by sea in search of gold, often burying the gold in hidden places throughout the Caribbean.