From about 1500 BC, bronze was gradually introduced, but the use of stone implements continued; Norway had few riches to barter for bronze goods, and the few finds consist mostly of elaborate weapons and brooches that only chieftains could afford. Huge burial cairns built close to the sea as far north as Harstad and also inland in the south are characteristic of this period. The motifs of the rock carvings differ slightly from those typical of the Stone Age. Representations of the Sun, animals, trees, weapons, ships, and people are all strongly stylised.