I think every town should have ancient defensive walls and a moat.
Not only are they pretty, but they're a gentle reminder that you are neither the first nor the last person on earth.
Chiang Mai's wall and moat are hundreds of years old, but the wall is only partial and is largely reconstructed. They form a square in the middle of town, so if you ever get lost you can just look for the wall and follow it around till you're found.
As a defensive strategy, however, the wall/moat combo was not a big success: Chiang Mai fell to the Burmese in 1556 and was ruled by a succession of conquerers for 200 years. It even sat empty for two decades in the late 1700s before finding its feet again as the unofficial capital of Northern Thailand.