Kaupang, a town from the Viking Age is believed to be the first town in Norway, although Tønsberg is the oldest town in Norway still existing.

Kaupang is mentioned under the name of Skiringssal (Kaupangen i Skiringssal) in Ohthere from Hålogaland's tales which date from the 9th century.

By the 10th century the local kings have established themselves as the first dynasty to begin the unification of Norway.

The king or his ombudsman resides in the old Royal Court at Sæheimr, today the Jarlsberg Estate (Jarlsberg Hovedgård) in Tønsberg.

The farm Haugar becomes the seat for Haugathing, the Thing for Vestfold and one of Norway's most important place for the proclamation of kings.The family of Harald Fairhair, who is most likely the first king of the whole Norway, is said to have come from this area.

At this time Vestfold, including Lier and Eiker, is a petty kingdom.