The Arch of Augustus (Italian: Arco d'Augusto, Romagnol: l’Èrc d’Augóst) is a gate set in the former city wall of Rimini, Emilia-Romagna, in the form of an ancient Roman triumphal arch.

Built in 27 BC in honour of Augustus, the first Roman emperor, the arch marks the northern end of the Via Flaminia, the road between Ariminum (Rimini) and Rome constructed in 220 BC by Gaius Flaminius. Under Fascist Italy, the adjoining city walls and surrounding buildings were demolished, leaving the Arch of Augustus to stand as an isolated monument.

The Arch of Augustus is the oldest preserved triumphal arch in Italy. Along with the Ponte di Tiberio, it is one of Rimini's most-recognised symbols, and is represented on the city's coat of arms. Because of the city's location at the tip of a strategically-important north–south passage by the Adriatic Sea, many armies have passed through the Arch of Augustus, leading Antonio Paolucci to describe the Arch of Augustus as "the eye of Italy's needle".

The arch was built in 27 BC, commissioned by the Roman Senate in honour of Augustus, who had become the first Roman emperor in the same year. It was built at the northern end of the Via Flaminia, a Roman road between Ariminum (modern Rimini) and Rome constructed in 220 BC by Gaius Flaminius, and at the start of Ariminum's decumanus maximus (Corso d'Augusto). The arch is functionally a city gate, and scholars deny that it was intended as a triumphal arch. The arch's construction coincided with a restoration of the Via Flaminia and the renaming of Ariminum as Colonia Augusta Ariminensis, leading the city to be associated with Augustus, a legacy that would be consolidated with the Ponte d'Augusto, completed in 21 AD, after Augustus' death, at the other end of the decumanus maximus. Outside the city walls, the arch led to a two-arched bridge onto the river Aprusa (Ausa), which was likely Augustan in origin, and repaired in late antiquity, the Middle Ages, and in the 17th and 18th centuries; it was expanded in the 1930s. The buildings near the arch were among the most elegantly-decorated of Ariminum.

The arch likely replaced an earlier gate about which little is known. The earlier gate would have been buried in thick cement. At its inauguration, the Arch of Augustus was flanked on either side by square defensive guard towers built at the time of Ariminum's foundation in 268 BC. Excavations in the 1980s recovered coins suggesting that the earliest yellow sandstone walls surrounding the arch dated to the 3rd century BC. In the 3rd century AD, the sandstone walls were supplanted by stone walls fitted with drainage arches. In the final phase of construction, sometime between the 3rd and 7th centuries, the original towers were replaced with seven-sided stone towers. These towers had a brick centre, composed of stone chippings mixed with mortar, and an outer stone casing. They are popularly attributed to the redesign of the city's urban fortifications under emperor Aurelian, and likely reached the height of the arch before being raised in later centuries.

From at least the third century, defensive gates were built immediately in front of and behind the Arch of Augustus. A 1541 report preparing the city for Pope Paul III's visit describes "two arches, one side by side, very ancient and built of large stones, and without much artistry". The fortified gates were likely demolished around the time of the visit, as part of an effort to remove ancient structures that obstructed the view of the Arch of Augustus. Its foundations are believed to be buried and rediscoverable by excavation.

In the Bavarian Code [it], a codex containing the church of Ravenna's investitures between the 8th and 10th centuries, the Arch of Augustus is called the Gate of Saint Gaudentius, after Gaudentius of Rimini, who was buried in a necropolis outside the city's walls.

Following the erection of new outer walls under Frederick II, the arch's military function declined from the mid-13th century. A medieval gate was built outside the Arch of Augustus, known as the Porta Romana (or the Gate of Saint Genesio or Saint Bartolo). The Porta Romana was destroyed after being seriously damaged by an earthquake in 1786.