There are apparently two arches built around 130 CE to honor Roman Emperor Hadrian—one in Athens and one in Jerash. The former is undoubtedly more studied, but the latter is objectively more beautiful! Maybe it's the color of the stones in the afternoon light, the unconventional architectural features, or just the sheer size of it.
In any case, it's hard to miss this large stone arch near the beginning of the Greco–Roman archaeological site as you enter Jerash. I recommend visiting in the morning or late afternoon hours, as the midday sun can be intense.