"Madoc: A Mystery", exploring themes of colonisation, is among Muldoon's most difficult works. It includes, as 'poetry', such non-literary constructions as maps and geometric diagrams. In the book "Irish Poetry since 1950", John Goodby states it is "by common consent, the most complex poem in modern Irish literature [...] – a massively ambitious, a historiographical metafiction". The post-modern poem narrates, in 233 sections (the same number as the number of Native American tribes), an alternative history in which Samuel Taylor Coleridge and Robert Southey come to America to found a utopian community. The two poets had, in reality, discussed but never undertaken this journey. Muldoon's poem is inspired by Southey's work "Madoc", about a legendary Welsh prince of that name. Critics are divided over the poem's success. Some are stunned by its scope and many others, such as John Banville, have professed themselves utterly baffled by it – feeling it to be wilfully obscure. Muldoon says of it: "I quite enjoy having fun. It's part of how it is, and who we are."