The erhu belongs to the huqin family of two-stringed fiddles, which were introduced into China by nomadic Mongols during the Yuan dynasty; the element hu in the name marks it as a foreign import. The bow hair passes between the two strings, and the instrument is played vertically on the knee, fingered with the left hand and bowed with the right. It is heard in traditional ensembles, modern orchestras and solo performance, and in opera.