Founded in 1946, the Juilliard String Quartet rose to international prominence following its 1948 American premiere of the complete cycle of Bartok's six string quartets. In its multiple incarnations since, the quartet has premiered the works of more than 60 American composers, championing the music of Elliott Carter, Roger Sessions, and Milton Babbitt; it rescued the quartets of Schoenberg from near obscurity and gave the first U.S. performance of Shostakovich's String Quartet no. 15, included on a 2006 recording that shows the current group's wide-ranging sonic capabilities. To celebrate its 60th anniversary, the quartet will present the Bartok cycle in two concerts this week. Tonight's program features the dark, highly chromatic First Quartet, the aggressive Third, and the Fifth--mature Bartok, modal and rhythmically driven, with a scherzo in the Bulgarian style. Tomorrow it's the Second, the exhilarating Fourth, and the hauntingly sad Sixth Quartet, the last work Bartok composed in his native Hungary. See also Wednesday. a 8 PM, Martin Theatre, Ravinia Festival, Green Bay & Lake Cook Rds., Highland Park, 847-266-5100, $10-$40.