Emona or Aemona, short for Colonia Iulia (A)emona, was a Roman castrum founded in 14/15 AD, possibly by the XV Legio Apollinaris (theory proposed by the noted historian and epigraphy expert Balduin Saria), on a territory already populated by ancient settlers of uncertain origin. Its location overlaps with the SW part of the old nucleus of the modern city of Ljubljana, capital of Slovenia, where numerous remains of Emona can still be seen today (substantial parts of the ancient city walls, most of which were destroyed in 1963, several mosaics, parts of the paleochristian baptistry, residential houses, statues, tombstones etc.).

(A)emona was, along with Nauportus, Celeia and Poetovio, one of the main cities on the eastern coast of the Adriatic. Formerly, it was assumed to have been a part of the Roman province of Pannonia. However, recent research seems to indicate that Aemona was actually the easternmost city of the Roman empire proper.

After few months of occupation in 388, citizens of Emona saluted Emperor Theodosius I entering the liberated city after the victorious Battle of the Save where Theodosius I defeated army of Roman usurper Magnus Maximus.

In 452, (A)emona was virtually destroyed by the Huns, led by Attila. Its remaining inhabitants fled the city; some of them made it to the coast of Istria where they founded a "second Emona", Aemonia, now the town of Novigrad (meaning "New City"), in Croatia.