Browning wrote “My Last Duchess” in iambic pentameter, meaning that the average line in the poem consists of five iambs. (Recall that an iamb has one unstressed syllable followed by a stressed syllable, as in the word “a-live.”) Iambic pentameter is the metrical form that most closely approximates the natural cadences of everyday speech in English. Considering that “My Last Duchess” is a monologue, the conversational quality of pentameter makes it an appropriate choice. In addition to sounding natural, many poets consider this meter to be the best choice for serious subjects because it also has a noble sound. Hence why rhyming pairs of iambic pentameter are also called “heroic couplets.” In this way, Browning’s use of pentameter gives the Duke’s speech an air of nobility that’s proper for his status. The poem takes a line before it fully enters an iambic groove, but afterward the meter is fairly regular. For a representative example, see lines 1–4:

     That’s my / last Duch- / ess paint- / ed on / the wall,
     Look-ing / as if / she were / a-live. / I call
     That piece / a won- / der, now; / Fra Pan- / dolf’s hands
     Worked bus- / i-ly / a day, / and there / she stands.

The first line opens with a trochee (stressed–unstressed) and a spondee (stressedstressed) before shifting to iambs. The first foot of the second line also opens with a trochee, but then quickly returns to iambic rhythm, which continues steadily for the next two lines.

Despite the general regularity of its meter, the poem has several deviations from strict iambic rhythm. Sometimes the deviations are obvious, as when Browning exchanges an iamb for a trochee. Other times the deviations are a bit subtler, as when Browning unexpectedly introduces punctuation in the middle of a foot. Line 55 exemplifies both types of deviation:

     Tam-ing / a sea-/ horse, thought / a rar- / i-ty

In addition to metrical variations, it’s also worth noting that the scansion of many lines in the poem are somewhat up for interpretation. The poem’s first line, for instance, could technically scan as strict iambic pentameter:

     That’s my / last Duch- / ess paint- / ed on / the wall

This interpretation places emphasis on the possessive adjective “my.” Such a reading makes sense insofar as it reflects the Duke’s sense of ownership and control. However, if we imagine him in the moment as he uses language to draw the emissary’s attention to the portrait, it also makes sense that he would stress the first word. Likewise, if we consider that the Duke is on his way to negotiate a new marriage, he might also stress “last” as a matter of distinguishing his previous Duchess from the prospective new one. Hence, the poem arguably begins with a trochee and a spondee:

     That’s my / last Duch- / ess paint- / ed on / the wall