The Roman city of Augustoritum Lemovicum, modern Limoges in France, founded 10 B.C. The most astounding feature of this important city (it had its own currency and senate even) is that it did not have any city walls. Abandoned after less than three centuries in late 3rd c. A.D. 
Its complete abandonment can be seen in the Roman street grid compared to the modern city. Not a single street matches. The location was excellent though, at an important ford (the "rito-" in its name—Augustoritum—is Gaulish for "ford").
The city is laid out on the standard Roman orthogonal grid, as all colonial cities are (as opposed to an organic grid of free- or feudal or ecclesiastical towns are. Major streets are colonnaded, with shops and eateries.
To avoid the dusty roads, the rear of the buildings face towards the green central courts and courtyards. A good spot to grow vegetables, herbs, for the household or the market. The streets have proper drains, maintained by the municipal teams (medieval streets maint. by owners).
The architecture is burnt or dried brick or timber frame with mud infill, town houses with two stories, some official buildings have three, but many houses are simple one story cottages. Note that there are no chimneys, smoke would have gone through the roof tiles.
The city had 25 000 inhabitants at its peak, thoroughly civilized with a huge central bath. When it was abandoned in 276 A.D. a reduced population moved together to Puy Saint-Etienne a few days travel to the east. By the 4th century less than 2000 people remained.
What killed the city? The story is familiar: the rich people moved out, preferring their country estates. Gradually the large villas were abandoned, the theatre stopped putting on shows, the baths stopped working. Whole neighborhoods were abandoned. Public maintenance stopped...
...and then barbarian invasions, 276 A.D. The noble country estates all sacked and burned, anarchy in the city itself. The economy ruined and no soldiers to call on for help, the few who remained left. Today only parts of the underground aqueduct survives, in medieval cellars.
