Complex sentence: The poem that made his reputation, "The Farmer's Boy", was written in a garret in Bell Alley where half a dozen other men were at work, and the finished lines he carried in his head until there was time to write them down.
Split into simpler sentences: The poem that made his reputation, "The Farmer's Boy", was composed in a garret in Bell Alley where half a dozen other men were at work. He carried finised lines in his head until there was time to write them down.