As the billing on the cover indicates, Chris Potter extends the creative envelope of his longstanding Underground Orchestra on his second date as a leader for ECM.

Guitarist Adam Rogers, drummer Nate Smith, and pianist Craig Taborn all return.

The additional architecture includes not one but two bassists in Scott Colley (acoustic) and Fima Ephron (electric).

Steve Nelson (Potter's former bandmate in Dave Holland's quintet) plays marimba and vibes, and a string quartet -- violinists Mark Feldman and Joyce Hammann, violist Lois Martin, and cellist David Eggar -- make this the "Underground Orchestra." "Lament" is introduced by the string quartet playing a near-Baroque melody before the jazz group enters with Rogers' warm, electric guitar.

Potter's first solo is moody as Nelson's vibes move toward modal terrain.

Colley's bridge-like solo is woody and rich.

Midway through, tempo and intensity shift, signified by Taborn and Smith.

Potter flies on tenor and the rest of the orchestra ups the tension and pulse in support before exiting on a pastoral theme.

The next 34 minutes are the four-part title suite.

While its sections tend to offer formal melodies and harmonics that are painstakingly charted over various jazz and classical languages, there is plenty of room for the players to stretch out.

"Pt.

1: Compassion" commences with the strings in a droning Eastern mode before a shadowy melody emerges.

By the time Rogers delivers his stinging yet tasteful solo, it becomes a grooving electric jazz workout.

"Pt.

2: Dualities" commences with a sprightly pizzicato string groove.

Potter takes the melody, then rips it up in a squalling solo, even as the strings -- now bowing -- foreshadow his harmonic movement.

By contrast, Nelson's solo is pure post-bop with excellent support from the rhythm section.

Taborn's spidery pointillistic inquiries introduce "Pt.

3: Disintegration," but it's the string quartet that shines, offering abstraction as a backbone for Potter and Rogers to emerge with an almost lush lyricism.

The final section, "Rebuilding," is a striking piece of grooved-out creative jazz.

Smith, Colley, and Ephron lock on as Taborn and Potter engage in muscular interplay.

Rogers' solo is the highlight, creating a bridge between parts as the strings offer not only color but harmonic direction.

Remarkably, there are three more pieces here, including the knotty, funky "Firefly," with Rogers offering as much textural flavor as a B-3 organ.

Closer "Sky" has a lush cinematic melody.

It's an excellent showcase for Potter, Taborn, and the string quartet, who all deliver excellent solos while keeping the tune's large landscape feel throughout -- one can hear traces of Aaron Copeland in some of its thematic lines.

Potter's writing on Imaginary Cities engages every aspect of his jazz palette.

It embraces modern classical music as part of a striking whole.

It is his most ambitious project to date, and arguably his most expertly articulated.