"When I returned from Spain and Gaul, in the consulship of Tiberius Nero and Publius Quintilius, after successful operations in those provinces, the senate voted in honour of my return the consecration of an altar to Pax Augusta in the Campus Martius, and on this altar it ordered the magistrates and priests and Vestal virgins to make annual sacrifice."
Augustus, Res Gestae (XII)
Indeed, Dio relates that the Senate initially "voted to place an altar in the senate-chamber itself, to commemorate the return of Augustus" (LIV.25.3). But nothing came of this idea and the Ara Pacis (Altar of Peace) was located on the northern part of the Campus Martius, where the army and cavalry maneuvered and an area that was becoming increasingly urbanized. Decreed in 13 BC, the altar was dedicated four years later in 9 BC to memorialize the peace which those conquests had brought to the empire. A square enclosure on a low platform with an altar in the center, the four marble walls are carved in relief and decorated with an arcanthus frieze. On the south wall, the imperial family is depicted in the procession that took place when the altar was consecrated.
Excavated and restored from hundreds of fragments in 1937-1938, on the occasion of Augustus' two thousandths anniversary, the Altar was relocated by the Tiber next to the Mausoleum of Augustus. Sixty years later, preliminary plans were presented for a new building, which opened in 2005.
"The course of my song hath led me to the altar of Peace. The day will be the second from the end of the month. Come, Peace, thy dainty tresses wreathed with Actian laurels [in honor of the end of civil war], and let thy gentle presence abide in the whole world. So but there be nor foes nor food for triumphs, thou shalt be unto our chiefs a glory greater than war. May the soldier bear arms only to check the armed aggressor, and may the fierce trumpet blare for naught but solemn pomp!"
Ovid, Fasti (January 30)
"This one is born for peace, that one is useful for the arms of the camp: everyone follows the seeds of his nature."
Propertius, Elegies (III.9.19)
If Augustus regarded himself as one born for peace, for the subjugated it was pacification by military conquest, as he himself proudly recorded. "The provinces of the Gauls, the Spains, and Germany, bounded by the ocean from Gades to the mouth of the Elbe, I reduced to a state of peace" (Res Gestae, XXVI).
References: Ara Pacis (2006) by Orietta Rossini; Res Gestae Divi Augusti (1924) translated by Frederick W. Shipley (Loeb Classical Library).
