What is "altar poem"

n. a visual poem in the shape of an altar or a cross

An altar poem is a type of poetry in which the lines are arranged in such a way that, when looked at as a whole, the poem forms the outline of an altar. The text and shape relate to each other, the latter usually giving added meaning to the poem itself. The tradition of shaped poetry goes back to Greek poets writing in Alexandria before the Common Era but most examples date from later and were written by European Christian poets during the Baroque period.