The correct answer is B. To defend against imperial challengers
Explanation:
The Castillo de San Marcos was a fort built by the Spanish in St. Agustine, Florida in 1672 as back then Florida territory was part of the Spanish Empire and not part of the U.S. The main purpose of this fort was to protect the city and the people in them from attacks led by other empires or by countries that wanted to take control of the territory. Indeed, the fort was built after an English raid in 1668 followed by two other attacks by the English after the fort was built. Additionally, after Florida became part of the U.S. the fort was used as a prison. Considering this, it can be concluded the purpose of the Castillo de San Marcos was to defend the city against imperial challengers.
