What is the purpose of a caesura in poetry?

A caesura is a slight pause in a line of poetry. Its purpose depends on the context of the words.

A caesura occurs in most lines poetry to break the line into 'chunks' of meaning, to extend meanings, to contrast ideas to produce rhythmic effects, etc. Usually there is a single caesura in a line, but there can be more. e.g. Oh dear, * she cried Why do I, so often, lie.