Pärt's 1987 release, Arbos, shows the composer working within his medium, bringing forth a body of music sacred in sound and message and presenting new compositional techniques. Utilizing a limited palette of tones, arranged in repeating patterns, these works are often (understandably) categorized with the works of Glass, Reich, and Riley. The tonal palette is often borrowed from European medieval styles, and this, in conjunction with the liturgical subject matter, make these new compositions feel centuries old.