These revolutionary works brought a strikingly organic — almost architectural — unity to the symphony that music historians recognized as far in advance of anything in the classical masters. Planted with seeds of change already evident in the beautiful, dark third symphony, the fourth symphony presented the most individual work in this form that the 20th century had yet witnessed. Harmonically new, boldly innovative, and structured on a subtle continuity of line, this was a kind of music previously unheard in the concert hall. Austere and intensely concentrated, Sibelius's symphonies of 1907 and 1911 are frequently performed around the world by major orchestras. "It is hard to think of any music in which the composer is more spontaneous and masterful, and uncompromising in his thought." Olin Downes, Thompson's International Cyclopedia.