After collecting material from literary sources, Borodin began composition in September 1869 with initial versions of Yaroslavna's arioso and Konchakovna's cavatina, and sketched the Polovtsian Dances and March of the Polovtsy. He soon began to have doubts and ceased composing. He expressed his misgivings in a letter to his wife: "There is too little drama here, and no movement ... To me, opera without drama, in the strict sense, is unnatural." This began a period of about four years in which he proceeded no further on "Prince Igor", but began diverting materials for the opera into his other works, the Symphony No. 2 in B minor (1869–1876) and the collaborative opera-ballet "Mlada" (1872).