Question about why Morro Castle (Fortress) in Havana, Cuba was built.?

I have to write a draft due tomorrow about Morro Castle (Fortress) and one of the things I have to write about is why it was built. On one website it says it was built in 1589 when Cuba was under the control of Spain but another website says it was built when the British successfully mined one of its bastions, When they handed Cuba back in 1763 to Spain, Morro Castle was built to prevent this from happening again. Please help! I don't know which one is write!!