These are postcards that show the historic city gates of the city of St. Augustine.
One of the images is of a “first day cover” marking the founding of St. Augustine in 1565. It incorrectly states that St. Augustine was the first permanent European settlement in the “New World” (i.e. the Americas), but that distinction goes to Santo Domingo, capital of the Dominican Republic, which was founded in 1496. St. Augustine is the oldest, continously inhabited settlement in North America.
The gate structure is what’s left of the walls that protected the city some 200 years ago. Constructed in 1808 to replace wood gates, they were part of the Cubo Line wall fortifications and were the only entrance into the city.