Thousands of rock carvings from this period depict ships, and the large stone burial monuments known as stone ships, suggest that ships and seafaring played an important role in the culture at large. The depicted ships most likely represent sewn plank built canoes used for warfare, fishing and trade. These ship types may have their origin as far back as the neolithic period and they continue into the Pre-Roman Iron Age, as exemplified by the Hjortspring boat.