Ministerial Decision G25871 of 9 July 1963 officially defined the EO1 as a major north-south route between Athens to the south and Evzonoi and the international border with the former Yugoslavia (now with North Macedonia) to the north: the decree specified that the EO1 would pass through Decelea, Sfendali [el], Martino, Atalanti, Kamena Vourla, Thermopylae, Lamia, Stylida, Almyros, Velestino, Larissa, Tempe, Katerini, Alexandreia, Chalkidona, Gefyra and Polykastro.

[1] Today, the A1 motorway has absorbed most of EO1's original alignment, although the EO1 continues to run alongside most of the A1 for non-motorway traffic.

However, there is a motorway-only gap west of Lake Yliki, requiring non-motorway traffic to detour via Thebes and Aliartos on the EO3.

Additionally, the border crossing itself, north of Evzoni, is only open to motorway traffic.

The EO1, as created by Ministerial Decision G25871 in 1963, was similar to the old EO1, which existed by royal decree from 1955 to 1963: however, the old EO1 followed the route of the current EO8 to Elefsina and then the EO3 up to Larissa, and the northernmost destination was Thessaloniki, instead of Polykastro and Evzonoi.