Across from the Acropolis, on one of the busiest streets in Athens, sits the ancient Temple of Olympian Zeus. The first temple was constructed early, maybe around 600 BC or earlier. The present temple was begun in the 5th century BC but wasn't completed until the 2nd century AD. It was one of the largest temples in antiquity.

At one end of the site stands Hadrian's Arch, which is the freestanding gate near the street. Hadrian had this gate erected when the temple was completed in the 2nd century AD; its purpose was to delineate the ancient city of Athens from the newer Roman city. On the side facing the Acropolis (and the ancient part of Athens), the inscription reads "This is the city of Theseus." On the side facing the temple (and the Roman part of Athens), the inscription says "This is the city of Hadrian and not of Theseus." The arch is Greek on top and Roman on the bottom.

See my blog post about the temple here.