Nine Ancient Roman columns believed to have originally lined the most important Roman road into the Balkans have been discovered on a riverbed in northern Italy.

''This is an extraordinary find because of the number of columns and the inscriptions they bear,'' local archaeological authorities said.

The stone columns are believed to date back to the fourth century AD and some carry inscriptions relating to the emperors of that late stage in the Roman Empire.

The columns are originally believed to have served as milestones along the road that led from Aquileia to ancient Aemona, today the Slovenian capital Ljubljana.

It was the main southwest route into the vast province of Pannonia which comprised most of today's Hungary, Croatia, Bosnia, Slovenia and Serbia.

At some stage in history, probably after the Empire fell, the pillars were moved to a bend in the river in which they were found, near Gorizia, archaeologists said.