Augustus
Augustus (Imperator Caesar Divi filius Augustus; 23 September 63 BC – 19 August AD 14) was a Roman statesman and military leader who became the first emperor of the Roman Empire, reigning from 27 BC until his death in AD 14. He was the first ruler of the Julio-Claudian dynasty. His status as the founder of the Roman Principate has consolidated an enduring legacy as one of the most effective and controversial leaders in human history. The reign of Augustus initiated an era of relative peace known as the "Pax Romana". The Roman world was largely free from large-scale conflict for more than two centuries, despite continuous wars of imperial expansion on the Empire's frontiers and the year-long civil war known as the "Year of the Four Emperors" over the imperial succession.
Augustus
Augustus was born Gaius Octavius into an old and wealthy equestrian branch of the plebeian "gens" Octavia. His maternal great-uncle Julius Caesar was assassinated in 44 BC, and Octavius was named in Caesar's will as his adopted son and heir, taking the name Octavian ( ). Along with Mark Antony and Marcus Lepidus, he formed the Second Triumvirate to defeat the assassins of Caesar. Following their victory at the Battle of Philippi, the Triumvirate divided the Roman Republic among themselves and ruled as "de facto" dictators. The Triumvirate was eventually torn apart by the competing ambitions of its members. Lepidus was driven into exile and stripped of his position, and Antony committed suicide following his defeat at the Battle of Actium by Octavian in 31 BC.
Cirta
Cirta, also known by various other names in antiquity, was the ancient Berber and Roman settlement which later became Constantine, Algeria. Cirta was the capital city of the Berber kingdom of Numidia; its strategically important port city was Russicada. Although Numidia was a key ally of the ancient Roman Republic during the Punic Wars (264–146BC), Cirta was subject to Roman invasions during the 2nd and 1st centuriesBC. Eventually it fell under Roman dominion during the time of Julius Caesar. Cirta was then repopulated with Roman colonists by Caesar and Augustus and was surrounded by a "confederation of free Roman cities" such as Tiddis, Cuicul, and Milevum. The city was destroyed in the beginning of the 4thcentury and was rebuilt by the Roman emperor Constantine the Great, who gave his name to the newly constructed city, Constantine. The Vandals damaged Cirta, but emperor Justinian I reconquered and improved the Roman city. It declined in importance after the Muslim invasions, but a small community continued at the site for several centuries. Its ruins are now an archaeological site.
Cirta
The town's Punic name krtn ( , probably pronounced "Kirthan", with a hard, breathy /tʰ/ sound) is probably "not" the Punic word meaning "town", which was written with a Q (i.e., qoph) rather than a K (kaph). Instead, it is likely a Punic transcription of an existing Berber placename. This was later Latinized as Cirta. Under Julius Caesar, the Sittian settlement was known as Respublica IIII Coloniarum Cirtensium; Pliny also knew it as Cirta Sittianorum ("Cirta of the Sittians"). Under Augustus, in 27 or 30, its official name was Colonia Julia Juvenalis Honoris et Virtutis Cirta; this was sometimes reduced to Cirta Julia ("Julian Cirta"), 'Colonia Cirta or simply Cirta. This name was rendered as by the historians Diodorus Siculus, Polybius, Appian, Cassius Dio, and Procopius and by the geographers Ptolemy and Strabo.

Question: Cirta was repopulated by Romans by the founder of what Roman empire?
Answer: Principate