What is "fratres"

Fratres, meaning “brothers” in Latin, is a composition by the Estonian composer Arvo Pärt exemplifying his tintinnabuli style of composition. It is three-part music, written in 1977, without fixed instrumentation — a “mesmerising set of variations on a six-bar theme combining frantic activity and sublime stillness that encapsulates Pärt’s observation that ‘the instant and eternity are struggling within us’.”