In 1223 Saint Francis of Assisi instructed his friars to adopt the form that was in use at the Papal Court ("Rule", chapter 3). They adapted this missal further to the needs of their largely itinerant apostolate. Pope Gregory IX considered, but did not put into effect, the idea of extending this missal, as revised by the Franciscans, to the whole Western Church; and in 1277 Pope Nicholas III ordered it to be accepted in all churches in the city of Rome. Its use spread throughout Europe, especially after the invention of the printing press; but the editors introduced variations of their own choosing, some of them substantial. Printing also favoured the spread of other liturgical texts of less certain orthodoxy. The Council of Trent determined that an end must be put to the resulting disparities.