Chantaburi's Catholic Cathedral of the Immaculate Conception, Thailand's largest Catholic cathedral, dominates the cityscape. Few visitors to Thailand have ever heard of Chanthaburi, a small provincial capital of a province by the same name, located about five hours east of Bangkok. But anyone with knowledge of the gemstone industry immediately knows the place. Once a source of high quality rubies and sapphires, Chanthaburi was forced to re-invent itself, as the area was heavily mined for its gemstones, in to what is now one of the most important trading centres in the world for coloured gemstones. As stocks plunged, Thais became experts in the heat treatment process which can turn an average or low grade gemstone in to a beauty, and as a result they set out across the world, mostly to Africa, to buy low quality gems for cheap which would then be brought back to Chantaburi and heat treated. From Friday until Sunday an area of downtown Chantaburi, covering several blocks, becomes packed with gem traders from across the globe, from Pakistan to China to Germany.