There are many examples of caesurae in Robert Browning's "My Last Duchess." The first appears in the third line:

That piece a wonder, now. Fra Pandolf's hands

The next glaring one is:

Are you to turn and ask thus. Sir, 'twas not

Then there are:

Or blush, at least. She thanked men,--good! but thanked
With anybody's gift. Who'd stoop to blame
Never to stoop. Oh sir, she smiled, no doubt,
Much the same smile? This grew; I gave commands:
As if alive. Will't please you rise? We'll meet
Together down, sir. Notice Neptune, though

And others.

Caesurae are customarily used in poetry for a pleasant aesthetic effect. But Browning is deliberately making the speaker of this poem appear crude and ignorant, although the Duke poses as a polished aristocrat and a connoisseur of art. Browning uses at least three means of creating a bad impression of the Duke. One, of course, is the content of his monologue, in which he tells how he apparently had his beautiful and affectionate young wife murdered.

The caesurae never lend aesthetic appeal to the lines in which they appear. They are abrupt, jarring, and insensitive. They contribute to an effect of raggedness which is unusual in what is supposed to be poetry.

Thirdly, it can easily be overlooked that the entire poem consists of rhyming couplets. But these are not the conventional closed couplets found in poems by authors like Alexander Pope and Samuel Johnson. The couplets in "My Last Duchess" are open and intentionally made lame and awkward in order to contribute further to the raggedness Browning was employing to characterize his speaker.

The very first two lines of the poem are a good example of the ungainliness of the rhyming:

That's my last Duchess painted on the wall
Looking as if she were alive. I call

(The Duke is also expressing himself badly. Some readers have assumed that the portrait was painted directly on the wall. Such a painting would deteriorate rapidly. What the ignorant Duke means is that the painting is on canvas and is hanging on the wall.)

There are so many bad rhymes in the poem that it is difficult to find one rhyming couplet that is not somehow offensive to the ear. Here are a few of the worst rhymes:

countenance/glance
durst/first
stuff/enough
whate'er/everywhere
breast/West
excuse/choose
meet/repeat
rarity/me!

Browning, of course, was a great poet. He was perfectly competent to write beautiful and graceful lines as well as to find appropriate rhymes. But in this unusual poem he chose to do just the opposite, to make the Duke seem crude and illiterate by his style of expressing himself as well as in the content of what he relates. He has the Duke himself confess that he is not a polished speaker:

Who'd stoop to blame
This sort of trifling? Even had you skill
In speech--(which I have not)--to make your will
Quite clear to such an one. . .

In the end the Duke has not succeeded in explaining what it was he objected to in his young wife. She seems lovely and admirable in every respect in spite of his criticism. Evidently what he objected to was the fact that she couldn't be as arrogant and wicked as he was--but, after all, he had had nine hundred years of inbreeding to perfect his hateful character.

Shakespeare has the Duke of Albany express a noteworthy truth about human nature in King Lear:

Wisdom and goodness to the vile seem vile:
Filths savor but themselves.   (IV.ii)