In the autumn of 1868, Vladimir Nikolsky, a professor of Russian history and language, and an authority on Pushkin, suggested to Mussorgsky the idea of composing an opera on the subject of Pushkin's "dramatic chronicle" "Boris Godunov". "Boris" the play, modelled on Shakespeare's histories, was written in 1825 and published in 1831, but was not approved for performance by the state censors until 1866, almost 30 years after the author's death. Production was permitted on condition that certain scenes were cut. Although enthusiasm for the work was high, Mussorgsky faced a seemingly insurmountable obstacle to his plans in that an Imperial ukaz of 1837 forbade the portrayal in opera of Russian Tsars (amended in 1872 to include only Romanov Tsars).