In many ways, the last volume in the ECM Rarum series of artist-chosen retrospectives is also one of its finest. Jon Christensen is the label's drummer of drummers. He has played with virtually every major leader on the roster, and his fluid, enigmatic touch has graced ECM's most outstanding recordings. Christensen has the rapacious appetite of an Elvin Jones or Roy Haynes, but combines it with the wondrously light, dancer's touch of a Billy Higgins. The nine tracks here showcase Christensen's uncanny ability to adapt, color, and in some cases even drive the vision of a bandleader toward its flourish. On the opening track, "Personal Mountains" (the title cut from a Keith Jarrett date with Jan Garberek and Palle Danielsson filling out the quartet), Christensen pushes Jarrett out of character, making the pianist hit the keys in direct response to the graceful yet furious attack coming from the kit. Alongside Ralph Towner on "Piscean Dance," a 12-string and drum duo, Christensen whispers incessantly, offering Towner the bedrock of force he needs to get physical with his guitar. On the funky "Per Ulev," led by Terje Rypdal, Christensen adds a shimmering Afro-Brazilian touch to his rhythm mélange and carries the track over. But it is on "Oceanus," from Towner's Solstice album with Garbarek, Eberhard Weber, and Towner, that Christensen is heard in his role of drummer as singing dancer. His double-timed whispering snare and cymbal work are accented with such sensitivity and motion that everyone plays off him. Towner fills the air with edgy chords and hammering runs on his 12-string as punched entries into the maelstrom as Garbarek articulates some far-off melody right into the kit. Weber, free not to worry about his end of time keeping, is free to engage with the other two as Christensen simultaneously holds the central space and moves it forward into near oblivion. But the most beautiful track on the entire set is the title track from Bobo Stenson's War Orphans from 1997. Christensen's place in the trio with the pianist and bassist Anders Jormin is one of melodist and harmonist. This is deeply moving music played with such care and dexterity that Christensen is all but completely unobtrusive, but provides the motion and dynamic for Stenson to articulate his open-field harmonic dexterity. In sum, Christensen's volume offers a rather stunning portrait of the ECM core roster, how exploratory and adventurous it has been since its inception, and continues to be. Highly recommended.