Although Celeia lived a relatively tranquil life during the Roman reign, far from the fierce battles, the peace would not last forever. Nomadic peoples from the east increasingly pushed against the eastern borders of the Roman Empire, which is also witnessed by the presence of the 2nd Italic Legion which set up a camp in the present-day Ločica pri Polzeli as early as in the mid-2nd century CE. At first, the walls were stormed by Marcomanni and Quadi. In 378, the town was under a fierce attack by the Goths. This was followed by the foray of the Alaric's army forty years later (408), and Attila's Huns in the mid-5th century (452) who succeeded in razing the Troia Secunda as Celeia was then picturesquely dubbed by its contemporaries, making the town the second Troy by its destiny as well.
Barbaric peoples pushing towards the lush and fertile Po Valley in the 6th century wreaked havoc. Indigenous population, or what was left of it, found refuge in remote and inaccessible areas, so-called refugiums. Although the name Celeia was still mentioned in those tempestuous times, the previously affluent town, then ravaged in the seventies of the 6th century, awaited the arrival of the Slavs. The town then lay in ruins and it was probable uninhabited.
In the years to come, its residents, stripped of all property, lived in poverty and struggled to survive. After the departure of the Lombards for Italy (568), this previously opulent area fell easy prey to the agricultural Slavs. The invasion that nobody stood up against was soon followed by consistent Slavic inhabitation, at first to the reduced cultivated lands along the Savinja River, and later on to more remote and less densely populated areas where the newcomers only found an odd indigenous inhabitant. Witnessing their presence to this day are some names for these virgin lands, such as Laško, Lahov graben, Lahovče etc.