Left to right: Benjamin Bagby, leiken, Jasmina Črnčič, and Norbert Rodenkirchen | Credit: Daniel Cullen At St. Mark's Episcopal Church on Thursday, June 11, the venerable early music ensemble Sequentia offered a mesmerizing program of 11th-century German songs, interspersed with purely instrumental works, exploring the Muses of classical antiquity and the art of music itself. It was the group's first appearance at the Berkeley Festival & Exhibition since 2018.