Desiderius (c. 720–786) was the last king of the Lombards, from 756 until the Frankish conquest of Pavia in 774.
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.