A fire hydrant (also known colloquially as a fire plug in the United States or as a johnny pump in New York City, because the firemen of the late 19th century were called Johnnies), is an active fire protection measure, and a source of water provided in most urban, suburban and rural areas with municipal water service to enable firefighters to tap into the municipal water supply to assist in extinguishing a fire. Buildings near a hydrant may qualify for an insurance discount since firefighters should be able to more rapidly extinguish a fire on the insured property. The concept of fire plugs dates to at least the 17th century. This was a time when firefighters responding to a call would dig down to the wooden water mains and hastily bore a hole to secure water to fight fires. The water would fill the hole creating a temporary well, and be transported from the well to the fire by bucket brigades or, later, by hand-pumped fire engines. The holes were then plugged with stoppers, normally redwood, which over time came to be known as fire plugs. The location of the plug would often be recorded or marked so that it could be reused in future fires. This is the source of the colloquial term fire plug still used for fire hydrants today. After the Great Fire of London in 1666, the city installed water mains with holes drilled at intervals, equipped with risers, allowing an access point to the wooden fire plugs from street level. The invention of a post- or pillar-type fire hydrant is generally credited to Frederick Graff Sr. , Chief Engineer of the Philadelphia Water Works around the year 1801. It had a combination hose/faucet outlet and was of "wet barrel" design with the valve in the top. It is said that Graff held the first patent for a fire hydrant, but this cannot be verified because the patent office in Washington D. C. caught on fire in 1836 destroying many patent records from that period in the process. In 1863, Birdsill Holly invented the modern version of the fire hydrant. While Holly was only one of many involved in the development of the fire hydrant, innovations he introduced are largely responsible for the fire hydrant taken for granted today. In 1869, Holly was issued U. S. patent #94749, for an "improved fire hydrant"