I have elsewhere quoted its beginning.

It is a fine example of his nature-poetry: it creates the scenery and atmosphere of the poem; and the four lines with which the fourth verse closes sketch what Browning thought to be one of his poetic gifts-- And mark through the winter afternoons.
By a gift God grants me now and then, In the mild decline of those suns like moons.
Who walked in Florence, besides her men.
This, then, is a poem of many moods, beginning with Giotto's Tower; then wondering why Giotto did not tell the poet who loved him so much that one of his pictures was lying hidden in a shop where some one else picked it up; then, thinking of all Giotto's followers, whose ghosts he imagines are wandering through Florence, sorrowing for the decay of their pictures.
"But at least they have escaped, and have their holiday in heaven, and do not care one straw for our praise or blame.

They did their work, they and the great masters.

We call them old Masters, but they were new in their time; their old Masters were the Greeks.

They broke away from the Greeks and revolutionised art into a new life.