In Roman times the Forum was surrounded by shops and public buildings and was the centre of the town. It was built during the reign of emperor Vespasian around the turn of 1st and 2nd centuries.
When I visited, parts of it was used as a parking lot....personally I don't like that way to use old Roman remainings.
The Roman Stadium was probably built during the reign of emperor Septimus Severus at the turn of the 2nd and 3th centuries. It had a capacity of more than 30.000 spectators. There are massive excavations going on there so it is nearly impossible to see anything of the stadium today.
The Ancient Forum was built during Roman times in I - II c. AD. While Plovdiv was part of the Roman Empire, it was called Thrimontium (City of Three Hills) and served as capital of the province of Thrace. Thrimontium was an important crossroad for the Roman Empire. "Via Militaris", the biggest military path in the Balkan Peninsula, passed through. The city had numerous public buildings, shrines, public bathrooms, theatres, etc.
These ruins are situated in downtown Plovdiv, near the central post office.