Complex sentence: Helge Ingstad and Anne Stine Ingstad carried out seven archaeological excavations from 1961 to 1968, investigating eight complete house sites as well as the remains of a ninth.
Split into simpler sentences: Helge Ingstad and Anne Stine Ingstad carried out seven archaeological excavations from 1961 to 1968. They investigated eight complete house sites as well as the remains of a ninth.