A community was usually an extended family. Its members lived a village in which a stone church was the most prominent building. They lived in one-room huts with walls and roofs made of wood, mud, and straw. Hangings covered the cracks in the walls to keep the wind out. Smoke from a fire in the middle of the room filtered out of cracks in the roof. Grain was ground at home by rotating by hand one stone disk on another stone disk. Some villages had a mill powered by the flow of water or by horses. All freeholders had the duty of watch [at night] and ward [during the day], of following the hue and cry to chase an offender, and of taking the oath of peace. These three duties were constant until 1195. Farmland surrounded the villages and was farmed by the community as a whole under the direction of a lord. There was silver, copper, iron, tin, gold, and various types of stones from remote lead mines and quarries in the nation. Silver pennies replaced the smaller scaetts. Freemen paid "scot" and bore "lot" according to their means for local purposes. Offa, the strongest of the Saxon kings, minted high-quality silver pennies. He traded woolen coats for lava grindstones with Emperor Charlemagne, who used a silver denarius coin. There were 12 denarii to the solidus and 20 soldi to the pound of silver. These denominations were taken by England as 12 pennies to the shilling and 20 shillings to the pound. The pound sign, an "L" with a hash mark derived from the word Libra, which meant weighing scales.