Whoever built the foundations of the walls of Mantinea did such a good job that despite the usual centuries of locals using the rest of the city as a quarry the outline of the city walls shows VERY VERY clearly in Google Earth.
This is a photo from 1907. The main difference I've seen in more recent shots is that in some sections less grass more wall.
Apparently there's been a lot of flooding in that area including lakes and rivers forming and disappearing as sinkholes in the area blocked and unblocked and so silt to the benefit of local farmers has built up around the walls. But such excellent walls!
Mantinea was originally Ptolis a settlement dating back to the Mycenaean age on a nearby hill now called Gourtsouli. The inhabitants moved down to the fertile plain and built a city.
That was centuries before the current surviving wall dating to about 370 BCE so possibly the walls follow or are on top on older ones probably the mud brick wall damaged by a water diversion during a siege in 385 BCE.
As with so many Greek polises most of the surviving structures are what little is left of an agora and stoa and council hall and a nearby theatre shown below.
There are several small villages nearby and the city of Tripoli which seems to absorbed what was left of the residents of Tegea Mantinea and other Arcadian cities in the 14th century.