Rondellus is a European ensemble dedicated to performing medieval and renaissance music using only period instruments. Based in the Estonian town of Tallinn, the group was founded in 1993 by husband-and-wife team Maria (vocals, hurdy-gurdy, organistrum) and Robert Staak (lute, percussion), who already shared a past in both academic music circles and in a local group called Hortus Musicus. After joining forces with vocalist Veikko Christian Kiiver, fiddler Tõnu Jõesaar, and Swedish singer and harper Miriam Andersén, they issued their first works as Rondellus in 1995, these being Secular Music in France from the XIVth-XVth Century and Sanctum Rosarium, which collected sacred songs from the Middle Ages containing themes of the Holy Rosary. Next came 1998's Carmina Sanctorium, featuring sacred music relating to medieval saints, after which the group decided to focus on performing and other pursuits for a while. Then, when approached by producer Mihkel Raud to record the seminal works of heavy metal godfathers Black Sabbath as if they'd been written during the Middle Ages, Rondellus rose to the challenge and made Sabbatum: Medieval Tribute to Black Sabbath look easy, transposing not only the music, but also all the lyrics so that they could be sung in Latin.