While there is no definite proof, there are compelling reasons to think the sport of racing pigeons may go back at least as far as 220 AD. Furthermore, it is recorded in the Mishnah that a pigeon racers are forbidden from bearing witness. The sport achieved a great deal of popularity in Belgium in the mid-19th century. The pigeon fanciers of Belgium were so taken with the hobby that they began to develop pigeons specially cultivated for fast flight and long endurance called "Voyageurs". From Belgium the modern version of the sport and the "Voyageurs" which the Flemish fanciers developed spread to most parts of the world. Once quite popular, the sport has experienced a downturn in participants in some parts of the world in recent years, possibly due to the rising cost of living, ageing fanciers, and a severe lack of public interest. Hypersensitivity pneumonitis is also a reason why some people are leaving the sport.