The Arch is a popular landmark that appears on many postcards. In the Athens area you can buy postcards showing the Arch during the day, the Arch at night, the Arch in the rain, the Arch in the snow, the Arch covered in vomit from drunken students, and so on.
According to A Postcard History of Athens, Georgia by Gary L. Doster, the Arch was cast in iron around 1856. It is a representation of the arch on Georgia's state seal, though the seal does not depict lamps at each end of the arch. These lamps on the University's Arch are only turned on for postcard photography season. Doster's account says that each of the pillars stand for Wisdom, Justice, and Moderation (Georgia's state motto), while another account says they represent the three branches of government. (Perhaps the motto was meant to describe the branches?)
The Arch, being the gateway that it is, is the site of much activity. At times you will find protesters gathered there or flowers laid on the steps for a memorial service.
One thing is certain: There is only one Arch. Perhaps inebriated people downtown see two on occasion, but there is really only one. Resist the urge to speak of "the arches" as many people do -- that will only encourage Georgia Tech fans to claim that people at UGA can't count.