Aigion — the ancient predecessor of modern Aigio — was founded in Homeric times and became one of twelve cities in the first Achaean League, the confederacy of Peloponnesian city-states that formed around 800 BC. When the Achaeans reformed their league in the third century BC and expelled the Macedonian garrison, they chose Aigion as their assembly place. The famous temple of Zeus Homarios stood here, and it was to this temple that delegates came to govern what was, for a time, the most significant political federation in the Greek world. The city produced Olympic champions: Xenophon, Ladas (stadion race), Athenodorus, Straton — names recorded in the ancient lists of victors. The Romans ended all of that in 146 BC. They dismantled the city walls and Aegium faded from its former prominence.

After centuries of Roman and then Byzantine rule, the city acquired a new name. By the ninth or tenth century it was being called Vostitsa — a name of debated origin, possibly Slavic, possibly meaning something like "fruit-bearing place." Crusaders captured it in the early thirteenth century and made it the seat of a barony within the Frankish Principality of Achaea. Ottoman forces took it in 1459, holding it with two brief Venetian interruptions until the Greek Revolution began. The city was one of the first to be liberated: Greek rebels captured it on 26 March 1821, just one day after the flag was raised at Agia Lavra monastery in the mountains above. The town formally reclaimed its ancient name, Aigio, after independence. In July 1822, fighters under Andreas Londos, Zaimis and Petimezas intercepted 4,000 Ottoman soldiers at nearby Akrata, driving them back to the sea.

For much of the nineteenth and twentieth centuries, Aigio's identity was agricultural and commercial. The area became one of the primary export hubs for Corinthian raisins — the small, intensely sweet dried grape called Zante currant in English, named for the island but grown extensively here. A 1903 geographic survey of Achaea estimated the region producing 7.5 to 10 million kilograms of raisins and 600,000 kilograms of olive oil annually. The port handled the trade, alongside Patras and Piraeus. Today the dynamic has shifted: Aigio's port now serves as a fruit import hub for Chiquita Brands International, primarily for bananas. A 256-meter pier completed in 2013 expanded the port's capacity. The raisins are still grown in the region, but the port's cargoes reflect how deeply global supply chains have rearranged what flows through old Achaean harbors.

On 15 June 1995, a serious earthquake struck Aigio, destroying buildings and damaging roads through the downtown and southwestern sections of the city. People died. Small memorials went up across the city afterward — with candles that are kept burning day and night — and they remain today. The earthquake did not erase the city; it added another layer to a place already dense with memory. Fires have complicated the landscape in the mountainous countryside nearby, severely in the 2007 Greek forest fires and in subsequent years as climate change has extended the fire season. The city rebuilds, as it has always rebuilt, on the same ground above the same gulf.

Walking through central Aigio today, you find layers compressed into a small space: neoclassical houses around Ypsila Alonia Square, its neogothic tower now housing a cafeteria; the Faneromeni cathedral, designed in 1914 by the Saxon-Greek architect Ernst Ziller; the Archaeological Museum of Aigion, also Ziller's work, built in 1890 in what was once the municipal market; and the shrine of Panagia Tripiti, built into a cliff thirty meters above the sea in a grove of cypresses and pines. The choreographer Hermes Pan — who worked with Fred Astaire on his great film musicals — was the American-born son of an emigrant from Aigio; he kept ties with family here. Since 2020, a new standard-gauge railway connects the city to Athens. The ancient assembly place of the Achaean League is a port town on a train line, still adding to itself.