Irish traditional music includes many kinds of songs, including drinking songs, ballads and laments, sung unaccompanied or with accompaniment by a variety of instruments. Traditional dance music includes reels (4/4), hornpipes and jigs (the common double jig is in 6/8 time). The polka arrived at the start of the nineteenth century, spread by itinerant dancing masters and mercenary soldiers, returning from Europe. Set dancing may have arrived in the eighteenth century. Later imported dance-signatures include the mazurka and the highlands (a sort of Irished version of the Scottish strathspey).