Oratorio del Caballero de Gracia is one of the best hidden architectural treasures in Madrid. This church looks small from the outside, but inside it unfolds into a neoclassical temple by Juan de Villanueva, which looks like a Roman basilica.
Among its most noteworthy internal features are the single-piece granite columns, the vault and the sculptures of the Virgen del Socorro, signed by Francisco Elías in 1825, and of Cristo de la Agonía, which, according to studies, was made by Juan Sánchez Barba in 1650. The church belongs to the Caballero de Gracia Eucharistic Association, founded by Jacobo Gratiis (known as the Caballero de Gracia), who was born in Modena in 1517 and who died in Madrid in 1619. It is currently run by Opus Dei.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.