The Roman theatre is the most visible remnant of Teramo's Roman past — the ancient Interamnia Praetuttiorum, founded in the early third century BC. The theatre dates from the first century AD and could seat around 3,000 people; the curved retaining wall of the cavea is still standing, embedded in the medieval and modern buildings around it.
The site is freely accessible from the small piazza alongside, with explanatory panels. The adjacent Roman amphitheatre, slightly larger but less well preserved, is a short walk away. Together they make a brief but evocative stop on a walk through the centre.