It was built in the 1960s as a replacement for the old National Road 8 as the major route to the Peloponnese, and bypasses most towns.

Its western end was the interchange with the A5 Ionia Odos, near Rio, northeast of Patras.

The section Corinth–Patras was the next to follow in 1969, as a 14m width undivided road (except for the Aigio bypass, which opened in 1973 also with motorway characteristics).

Between 1997 and 2015, the expanded section ended near Corinth, from which it continued as a limited-access single carriageway.

The remainder, between Kiato and Rio, was opened in April 2017,[1] and the EO8a has ceased to exist.