External frame packs were designed to carry heavy loads (>20 kg or 40 lb). This gives the wearer more support and protection and distributes weight better. Wooden pack frames were used for a long time around the world. Ötzi the Iceman may have used one in Copper Age Alpine Italy. But some archaeologists think the frame found with the body was part of a snowshoe. These packs are common in military and mountaineering. Metal packs first appeared in the mid-20th century.