Generally, the seven wonders of the medieval world are considered to be Stonehenge, the Colosseum, the Catacombs of Kom el Shoqafa, the Great Wall of China, the Porcelain Tower of Nanjing, the Hagia Sophia and the Leaning Tower of Pisa. Some lists of the wonders substitute the Taj Mahal, the Cairo Citadel, the Ely Cathedral or the Cluny Abbey.
Although the majority of the wonders of the medieval world were already built prior to the de facto Middle Ages, dated by historians as the period from the fifth to 15th centuries A.D., each structure survived or was improved during the era. Stonehenge, for example, was likely built around 2,000 B.C. by indigenous Celts of Britain, and it was well-known and studied by scholars of the Middle Ages. Similarly, the Great Wall of China was built in several phases beginning in the eighth century B.C., culminating in its greatest length in the late 17th century A.D.
The format for lists of wonders of the world dates to Greek texts of the first and second century B.C. that describe the seven wonders of the ancient world: the Great Pyramid of Giza, the Hanging Gardens of Babylon, the Temple of Artemis, the Statue of Zeus at Olympia, the Mausoleum of Halicarnassus, the Colossus of Rhodes and the Lighthouse of Alexandria.