Britain has the longest known continuous patent system. British patents can be traced to the 15th Century, when the British Crown began granting exclusive rights, called “Letters Patent,” to certain manufacturers and traders. The Crown granted monopolies for the manufacture and sale of products such as soap, leather, glass, knives, starch, iron and paper. These “patents” were literally letters marked with the seal of the Crown and they granted an exclusive right to make and sell the item described in the letter for the period of time set forth in the letter. There was no novelty, non-obviousness, or other patentability requirement as there is today. Patents were often granted for inventions that were not new, usually to friends of the Crown or for the purpose of collecting revenues without direct taxation of British citizens. One of the earliest British patents, granted by King Henry VI to John of Utynam in 1449, was a 20-year monopoly for a method of making stained glass.