13th century, the trading of coal increased across Britain and by the end of the century most of the coalfields in England, Scotland and Wales were being worked on a small scale. As the use of coal amongst the artisans became more widespread, it became clear that coal smoke was detrimental to health and the increasing pollution in London led to much unrest and agitation. As a result of this, a Royal proclamation was issued in 1306 prohibiting artificers of London from using sea coal in their furnaces and commanding them to return to the traditional fuels of wood and charcoal. Marco Polo wrote about the widespread use of coal in Yuan dynasty China in the late 13th century in The Travels of Marco Polo, remarking that coal was the primary fuel of the land and that it helped support heated baths for the citizenry beyond what wood would be able to do. During the first half of the 14th century coal began to be used for domestic heating in coal producing areas of Britain, as improvements were made in the design of domestic hearths. Edward III was the first king to take an interest in the coal trade of the north east, issuing a number of writs to regulate the trade and allowing the export of coal to Calais. The demand for coal steadily increased in Britain during the 15th century, but it was still mainly being used in the mining districts, in coastal towns or being exported to continental Europe. However, by the middle of the 16th century supplies of wood were beginning to fail in Britain and the use of coal as a domestic fuel rapidly expanded. In 1575, Sir George Bruce of Carnock of Culross, Scotland, opened the first coal mine to extract coal from a "moat pit" under the sea on the Firth of Forth. He constructed an artificial loading island into which he sank a 40 ft shaft that connected to another two shafts for drainage and improved ventilation. The technology was far in advance of any coal mining method in the late medieval period and was considered one of the industrial wonders of the age. During the 17th century a number of advances in mining techniques were made, such the use of test boring to find suitable deposits and chain pumps, driven by water wheels, to drain the collieries. People who sold wood,