by Ross Boissoneau The vocalists for Riverdance were Celtic stars before Michael Flatley & Co. blazed across the stages of the world, and Invocation demonstrates why. The music on Invocation dates from as far back as the sixth century and up through the years to the relatively modern 19th century. Regardless of its age, it all sounds ancient and powerful, even at its most fragile. The best Celtic music transcends time and language, and this is some of the best -- simply magical, from the first note to the last. A mesmerizing blend of voice with minimal instrumentation.