The Vielle a Roux (or hurdy gurdy) is a stringed instrument which is sounded by the rubbing of a wheel against the strings. The wheel is turned by a crank and functions in a similar way to a bow. Translated from the French it's name means 'wheel fiddle'. It is commonly known as a hurdy-gurdy in English and also a drehleier or radleier in German.
It was believed to have originated sometime prior to the 11th century in Europe and was a common instrument throughout Europe from the 12th to 19th centuries. One of the earliest forms of the hurdy gurdy was the organistrum, a larger instrument that was played by 2 people. The French court adopted the Vielle a Roux in the early 18th century and their version of the instrument became the standard, although traditional variations persist in other European countries.
The wheel is turned by the player's right hand, while the left hand plays the tune using the keys in the keybox. Commonly two of the strings are called 'chanters' (or melody strings) and run though the keybox. Their vibrating length is shortened by the pressure of the key against them. The other 'drone' strings are exterior to the keybox, and sound a constant pitch. A small, movable bridge on one of the drone strings can be made to vibrate rhythmically by cranking the wheel harder creating a rhythmic accompaniment to the melody. The constant sound of the drone strings gives the instrument a sound similar to a bagpipe.