The most profound European influence is that of Spain, the island's colonizer. Spanish influence is the most notable of all cultural influences in Puerto Rican culture. Spanish heritage has left an indelible mark on the island, and signs of this cultural exchange can be found everywhere, from the Colonial architecture and official language to the island's literature and local culinary styles. As far back as the 16th century, the Spanish built a series of massive defense structures to protect Old San Juan and its bay from other invaders. Parts of Old San Juan and La Fortaleza are now UNESCO World Heritage Sites.