For decades after the conquest, the Roman presence in Greece was informal. Local Greek communities scrambled to establish formal treaties of "friendship and alliance" with Rome — not because they loved the arrangement, but because Roman patronage offered protection against their neighbors. Inscriptions record such treaties with Epidaurus and Troezen in the late 2nd century BC, with Astypalaea in 105 BC, with Thyrium in 94 BC. Rome increasingly served as arbitrator in Greek disputes, usually favouring those already tied to it by treaty. The formal province of Achaia took definitive shape under Augustus in 27 BC, when he separated Greece, Thessaly, and part of Epirus from Macedonia to create a senatorial province governed from Corinth — the city Caesar had refounded as a Roman colony in the 40s BC, forty-six years after his predecessors had razed it to the ground. Before that, the civil wars of the Late Republic had turned Greek soil into a Roman battlefield: Pharsalus in 48 BC, Philippi in 42 BC, Actium in 31 BC. The Achaians had endured centuries of Greek interstate warfare; now they watched Roman factions settle their quarrels on the same plains.

The relationship between Rome and Greece was never purely administrative. Nero visited in AD 66 and performed at the Ancient Olympic Games, despite rules prohibiting non-Greek participation. He was declared victor in every contest he entered. The following year, at the Isthmian Games in Corinth, he proclaimed the freedom of the Greeks — a gesture Flamininus had made over two centuries earlier. Vespasian cancelled the grant and reportedly quipped that the Greeks had forgotten how to be free. Hadrian, who reigned from 117 to 138, was more genuinely devoted. He had served as an eponymous archon of Athens before becoming emperor. He completed the Temple of Olympian Zeus, which had stood unfinished for centuries, reformed the Athenian constitution, and created a Panhellenic council where representatives of all Greek states met under Athenian leadership. The Athenians built the Arch of Hadrian in return. Herodes Atticus, an Athenian who became one of the wealthiest men in the empire, funded monuments across Greece during this period — a Greek magnate operating comfortably within the Roman imperial elite.

The Pax Romana was, as the Wikipedia source notes, the longest period of peace in Greek history. That peace made Greece a crossroads of maritime trade connecting Rome with the Greek-speaking east. The Greek language itself continued as the effective lingua franca of the eastern empire; Greek intellectuals like the physician Galen did their most celebrated work in Rome rather than Athens. Into this world walked the apostle Paul of Tarsus, who preached in Philippi, Corinth, and Athens. In the opening lines of his Second Letter to the Corinthians, he addressed "all the saints who are in the whole of Achaia" — using the Roman provincial name as a natural geographic designation. Greece became one of the most rapidly Christianised regions of the empire, a transformation that would prove far more durable than any administrative boundary.

The Pax Romana was not permanent. In 170 or 171, during the Marcomannic Wars, the Costoboci swept south through the Balkans into Achaia, sacking the sanctuary of Demeter and Persephone at Eleusis — one of the holiest sites in the Greek world. A Roman procurator arrived with a small force to clear them out. In 267, the Heruli led a naval raid through the Aegean, plundering Sparta, Corinth, Argos, and the sanctuary of Zeus at Olympia before sacking Athens. The Athenian historian Dexippus rallied a local force and eventually drove them off. In the aftermath, classical monuments throughout Athens were dismantled and their stone used to build a new defensive wall, which enclosed only a small area around the Acropolis. Greece was invaded again in 395 by the Visigoths under Alaric, who looted Athens, Corinth, and the Peloponnese before being driven out. Yet the province survived. Recent archaeological work has substantially revised older images of a late-antique Greece in terminal decline. The polis, as an institution, remained viable into the 6th century, and a contemporary source — Hierokles' Syndekmos — describes a late-antique Greece with approximately eighty functioning cities.

Throughout the province's history, Corinth served as its administrative heart. Positioned on the narrow isthmus connecting mainland Greece to the Peloponnese, it controlled overland traffic between north and south and the maritime trade routes of both the Saronic and Corinthian gulfs. Roman Corinth was a colonial city, Latin in its early character, but it Hellenised rapidly and became one of the most prosperous urban centres in the east. Paul's letters to its community are among the earliest documents of urban Christianity. Hadrian's aqueduct still threads through the landscape nearby. The stones of the ancient forum still lie in the shadow of the seven surviving columns of the Temple of Apollo, which stood before the Romans came and endured long after they left.