Complex sentence: The title is an allusion to Dante's first circle of Hell in The Divine Comedy-wherein the Philosophers of Greece live in a walled green garden-unable to enter heaven, but enjoying a small space of relative freedom in the heart of Hell.
Split into simpler sentences: The title is an allusion to Dante's first circle of Hell in The Divine Comedy, wherein the philosophers of Greece live in a walled green garden. They are unable to enter Heaven, but enjoy a small space of relative freedom in the heart of Hell.