Guard Tower Royalty-Free Stock Photography

Sentry box at Fort San Cristobal in Old San Juan, Pto. Rico. Its construction began in 1634 and when it was completed about 150 years later, it became the largest fortification built by Spanish settlers in the Americas. It has an extensive network of tunnels that made it easier for soldiers to get around the fort. Towards the end of the 19th century, a rather large portion of the fort was destroyed to allow the city of San Juan to expand, but all of the main attractions remain (the main plaza, or Plaza de Armas, the sentry boxes, the chapel, the tunnels and the soldiers' quarters.