When I beheld the Poet blind, yet bold,
In slender Book his vast Design unfold,
Messiah Crown'd, Gods Reconcil'd Decree,
Rebelling Angels, the Forbidden Tree,
Milton began losing his vision as early as 1644, and by 1652 had gone completely blind. The cause of his blindness has been subject to medical debate, though likely it was either glaucoma or bilateral retinal detachment. With his failing eyesight, Milton had to dictate his writing to a string of secretaries, one of whom was Marvell.
On Mr. Miltons Paradise Lost