Fodor's Expert Review Walls of Rhodes
One of the great medieval monuments in the Mediterranean, the walls of Rhodes are wonderfully restored and illustrate the engineering capabilities as well as the financial and human resources available to the Knights of St. John. For 200 years the knights strengthened the walls by thickening them, up to 40 feet in places, and curving them so as to deflect cannonballs. The moat between the inner and outer walls never contained water; it was a device to prevent invaders from constructing siege towers. You can get a sense of the enclosed city's massive scale by walking inside the moat.
Parts of the walkway that runs the 4 km (2½ miles) along the top of the walls is sometimes accessible through the Palace of the Grand Master by a city tour; check with the Rhodes tourist office for times.