27. Theodosian Walls of Might
The massive set of double walls, built under the reign of Theodosius II, became rightly known as the Theodosian Walls. They were considered a marvel of their age, and still highly respected by historians and archaeologists for being an early engineering and construction marvel. The walls withstood numerous sieges through the centuries and were only finally bested by the inventions of gunpowder and cannons.
