Mosaics and frescos in the Chora Church date from the beginning of the 14th century. They are breathtaking. Despite centuries of neglect and intentional defacing (that means cutting off the faces if your religion says no images) -- the artworks have survived. The fresco below shows Jesus pulling Adam and Eve out of their graves.
Here is the Byzantine city wall near the church. For its first 80 years, many centuries ago, the church was outside the wall, but this wall -- from the Golden Horn to the Sea of Marmara -- soon enclosed a greater Constantinople: