Free Verse
"The Colossus" doesn't follow any particular meter. Its haunting images come in fairly conversational free verse. Still, the stanzas are all pretty tidy, with each having five lines. Why five lines exactly? Well, the generally tidy appearance of the poem mirrors the way the speaker is trying to tidy the ruins of the statue. Despite all this tidiness, however, another thing the poem does structurally is become a little more disjointed as it goes along. Check out how the fourth stanza begins:
A blue sky out of the Oresteia
Arches above us. O father, all by yourself (16-17)
Notice, how we get a period right in the middle of 17, creating a pause (or caesura) smack dab in the middle of the line. Yeah, that hasn't happened before in the poem (and it won't again actually). Having the pause right before "O father" really makes it pop in our mind's ear (if you follow), which works well since the father is what the whole poem seems to be about.
The end of the fourth stanza also spills over into the next:
I open my lunch on a hill of black cypress.
Your fluted bones and acanthine hair are littered
In their old anarchy to the horizon-line.
It would take more than a lightning-stroke (19-22)
This is the first place in the poem that does this and it continues in the transition from fifth to the sixth and final stanza:
Nights, I squat in the cornucopia
Of your left ear, out of the wind,
Counting the red stars and those of plum-color.
The sun rises under the pillar of your tongue. (24-27)
By having these thoughts visually broken up on the page, the poem starts to feel more and more fractured, which not only mimics the shattered ruins of the statue, but also the damaged psyche of the speaker.