The Kaarli Church (or Charles XI’s Church) was built between 1862-1882 to replace the original Kaarli Church, itself founded in 1670 on the order of Sweden's King Charles XI. Like many wooden structures located outside the city wall, the first Kaarli Church burned down during the Great Northern War in the early 1700s.
Architect Otto Pius Hippius from St. Petersburg built the present limestone church using a special arch technique that gave it have a vast, open interior. With its wonderful acoustics and seating capacity of 1,500, the church is often used as a venue for choral concerts.
The Kaarli Church is home to the first Estonian fresco, “Come to Me,” painted in 1879 by famed Tallinn artist Johann Köler. It also boasts the country's largest church organ, installed in 1924.
Reference: Tallinn Tourism
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.