The Carolingian conquest of northern Italy in 774 put an end to the Kingdom of the Lombards.
The “Historia Langobardorum” is the oldest chronicle relevant to the history of Venice. It probably dates to the 780s or 790s.
In late Antiquity the north-east of the Italian peninsula suffered many invasions. The wars caused people to move to the safer lagoon areas, and hence to the foundation of Venice.