You walk beneath the triple arch dedicated to Augustus by the Senate to honor his recovery of the standards, particularly the legionary eagle, lost to the Parthians in 53 BCE by Crassus (who also lost his head). Julius Caesar had been assassinated before he could recover the standards, and Antony had been unsuccessful in his efforts to defeat the Parthians, but when Augustus marched to the east in 19 BCE, the Parthian king Phraates returned the standards and surrendered to Rome, a major victory for the new emperor. The arch was topped Augustus driving a four-horse chariot and images of the Parthians surrendering the standards The inscription on this coin reads reads CIVIB[us] ET SIGN[is] MILIT[is] A PART[hiis] RECVPER[atis] ("for the citizens and military standards recovered from the Parthians"). See this reconstruction of the arch looking toward the Forum, courtesy of UCLA's Digital Roman Forum).
To follow Tristia Tresunus to his third stop, take the Temple of Vesta exit.