This thesis studies ritual interactions between saints and the landscape, animals and elements during a three-hundred year period from 410 AD. Such interactions include negotiations about and with birds and other animals, exorcism of the sea, lakes and rivers, and immersion in these natural bodies of water for devotional purposes. Although writers of the period lacked a term such as 'nature' to describe this sphere of activity, it is demonstrated that the natural world was regarded as a dimension of creation distinctively responsive to Christian ritual. Systematic study of the context in which these rituals were performed finds close connection with missionary negotiations aimed at lay people. It further reveals that three British writers borrowed from Sulpicius Severus' accounts of eastern hermits, reworking older narratives to suggest that non-human aspects of creation were not only attracted to saints but were changed by and participated in Christian ritual and worship. Natural bodies of water attracted particularly intense interaction in the form of exorcism and bathing, sufficiently widely documented to indicate a number of discrete families of ritual were developed. In northern Britain, acute anxieties can be detected about the cultural and spiritual associations of open water, requiring missionary intervention to challenge pre-Christian narratives through biblical and liturgical resources, most notably baptism. Such a cosmological stretch appears to have informed a 'Celtic' deviation in baptismal practice that emphasised exorcism and bodily sacrifice. Nature rituals were a systematic response to the challenges of the British intellectual and physical landscapes, revealing the shape of an underlying missionary strategy based on mainstream patristic theology about the marred relationship between humans and the rest of creation. St Ambrose emerges as the most influential theologian at the time when the early church was shaping its British inculturation, most notably led by St Germanus' mission in 429.