Final answer:
The Pompeian amphitheatre was built by Gaius Quinctius Valgus and Marcus Porcius in 70 BCE and had a seating capacity of up to 24,000 spectators.
Step-by-step explanation:
The Pompeian amphitheatre, considered the first stone amphitheatre, was constructed in 70 BCE. It was built by Gaius Quinctius Valgus and Marcus Porcius, who were duumvirs at the time. These notable figures were responsible for overseeing the construction at their own expense and dedicated it to the colonists in perpetuity. The amphitheatre could seat up to 24,000 spectators, approximately the entire population of Pompeii at the time, and serves as a significant example of Roman engineering and cultural importance.