You see before you a large complex structure: a rectangular quadriporticus is connected on its western side to Rome's first permanent stone theater, constructed in 55 B.C. Gnaeus Pompey had the complex built to celebrate his triple triumph in 61 B.C.
By the end of the 1st century BCE three permanent stone theaters of different sizes -- and probably intended for different types of ludi (spectacles) -- had been constructed in the Campus Martius. The largest (and throughout history the favorite with the Romans) was built by Pompey (see Theatre of Pompey Project); the other two, smaller in size, were built as part of Augustus's building program.
Pompey's Quadriporticus