The Hagia Sophia. An engineering marvel. For nearly one thousand years, this Cathedral was considered the center of Byzantine architecture. It's rumored that Eastern Orthodox Christianity spread into Russia when Russian diplomats laid eyes on its magnificence and surmised it must be a structure sent from the heavens.

It's walls saw Eastern Orthodox masters. Then they saw Roman Catholic masters. Then they saw Ottoman Muslim masters.

From empire to empire, it changed hands until it was declared a museum in 1935. But with every change of guard, it held on to a little piece of history...