When the Romans defeated the Greeks in the 2nd century BC, they wanted their own meeting place and market, so they built a Roman-style forum near the former Greek Agora. The Emperor Hadrian was the brains behind this project; in his honor the site contained a library (known today as Hadrian's Library), the remnants of which you can still see. The real gem, though, is the Tower of the Winds, built in the 1st century BC by an astronomer as a sundial and water-powered clock, with relief sculptures of the winds on its sides.
The Romans valued the Greeks' knowledge and sent many of their sons to be educated in Athens. Under this Roman rule, the Greeks had 300 years of peace, the longest in their history.
The Roman Forum is located north of the Acropolis. Enter from the corner of Pelopida and Eolou Streets. Nearest metro is Acropolis. From the Roman Agora walk in the emperor's footsteps by following Adrianou (Hadrian's) Street to Hadrian's Arch.