Significance. La Fortaleza (The Fortress) was the first true fortification in San Juan, established in 152l. The Spanish built it between 1533 and 1540 for protection against raids by Carib Indians and by English and French freebooters.Explorers and Settlers (La Fortaleza) - National Park Servicenps : parkhistory : online_books : explorers : sitec58freebet unibet code centros de apostas on line