Augustine's De Trinitate is a theological work written by Saint Augustine in the early 5th century that explores the nature of the Holy Trinity. In this work, Augustine seeks to articulate a coherent understanding of the relationship between the Father, Son, and Holy Spirit, emphasizing their unity and distinctiveness. This text is significant in the historical development of Trinitarian theology as it provides one of the earliest comprehensive examinations of the Trinity, which has influenced Christian thought for centuries.