By Madison Marrone
If all the pauses in a poem occured at the end of the line, the sound of it could become dull. Moving these pauses so they occur within the line creates a musical tone and therefore increases the interest level of the poem.
A caesura is formed by the rhythms of natural speech rather than by metrics. It will usually occur near the middle of a poetic line, but can also occur at the beginning or the end of a line. In poetry, there are two types of caesural breaks: feminine and masculine.
An Essay on Man by Alexander Pope
Know then thyself II, presume not God to scan;
The proper study of Mankind II is Man.
Plac'd on this isthmus of a middle state,
A being darkly wise, and rudely great:
Winter's Tale by Shakespeare
It is for you we speak, || not for ourselves:
You are abused || and by some putter-on
That will be damn'd for't; || would I knew the villain,
I would land-damn him. || Be she honour-flaw'd,
I have three daughters; || the eldest is eleven
The second and the third, || nine, || and some five;
If this prove true, || they'll pay for't. || By mine honour. (Act II, sc. I :142-148)