This superb pair of Late Roman helmets were found in 1955 in Berkasovo, Serbia, near the Roman settlement of Sirmium (modern-day Sremska Mitrovica). The site itself dates back to at least the 4th century BC, mentioned as being occupied by Illyrians and Celts, before the Romans conquered the province in the 1st century BC. Sirmium was declared capital of the province of Pannonia at this time. The city was later elevated to the status of one of the four imperial capitals in AD 294.
The settlement was also the home of the praetorian prefecture of Illyricum as of AD 347 (a prefecture being the largest administrative division of land in the late Roman world, of which there were four), making Sirmium an important settlement in the Roman Empire for centuries. It also boasted a population of allegedly 100,000, although more conservative estimates suggest 7,000 (however the amount of grain imported between AD 1 and AD 400 seems a suitable amount to have fed between 700,000 and 1,000,000 inhabitants). The modern region of Syrmia (Srem) was named after Sirmium. Sirmium was also birthplace to several Roman Emperors, including Aurelian, was the site at which Theodosius I (the last emperor of a unified empire) was crowned, and proved a popular visiting spot for others including Marcus Aurelius who may even have died in the city in AD 180.
Berkasovo herself is a smaller village less than one hour from Sirmium, likely a small village at the time or possibly a mansio (a rest point along a major road, incorporating a small inn, stables, and accommodation). One source suggests the helmets were deposited in what seems to be a Roman pantry, which would fit this theory rather neatly.
As Sirmium and the surrounding region became overtaken by Gothic tribes in the latter half of the 4th century, it seems reasonable to suggest that these helmets are dated to the earlier half of the 4th Century.