The Hippodrome of Domitian is shaped like a Roman circus. However, it cannot have been used for hair racing as it is too small. One theory indicates that it was used for foot races, while another argues that it was only built as a decoration for a garden. You have all the information in: «Rome tourist guide: what to see, itineraries and recommendations«.
You have all the information in: "Rome tourist guide: what to see, itineraries and recommendations".