Arch of Titus in Rome.
A triumphal arch is a free-standing monumental gateway of a type which originated in Rome in the second century BC in richly decorated temporary structures erected by Roman magistrates for such festive occasions as the triumphs decreed to victorious generals.
From the late first century BC similar structures were erected in stone, and often richly decorated with sculpture, as city gates or as entrances to fora but also frequently as urban decorations with no more than a commemorative purpose: some twenty survive from the reign of Augustus, mostly in Italy and Gaul. They were built throughout the Roman Empire and numerous 2nd and 3rd century AD examples survive in North Africa. There are two main types – those with a single archway (Arch of Augustus at Susa, Piedmont, 9–8 BC, Arch of Titus in Rome, c. AD 82) and those with a large archway flanked by two small archways (Arch of Septimius Severus in Rome, AD 203, and Arch of Constantine in Rome, AD 315). Sometimes they seem to have been designed primarily as richly ornamented bases for gilt bronze statues. The form was revived in the Italian Renaissance.