The Siege of Paris and the Sack of Paris of 845 is the culmination of a Viking invasion of the kingdom of the West Franks.

The Viking forces are led by a Danish chieftain named "Reginherus", or Ragnar, who traditionally has been identified with the legendary saga character Ragnar Lodbrok.

Ragnar's fleet of 120 Viking ships, containing thousands of men, enters the Seine in March and proceeds to sail up the river.

The West Frankish king Charles the Bald assembles a smaller army in response, but as the Vikings defeat one division, comprising half of the army, the remaining forces retreat.

The Vikings reach Paris at the end of the month, during Easter.

After plundering and occupying the city, the Vikings finally withdraw after receiving a ransom payment of 7,000 French livres, or pounds (2,570 kilograms (5,670 lb)) of silver and gold from Charles the Bald.