The massive ancient earthwork that provides the sole commemoration of an extraordinary Anglo-Saxon king and that gives its name to one of our most popular contemporary national walking trails remains an enigma. Despite over a century of study, we still do not fully understand how or why Britain's largest linear monument was built, and in recent years, the views of those who have studied the Dyke have diverged even as to such basic questions as its physical extent and date of construction. This book provides a fresh perspective on the creation of Offa's Dyke arising from over a decade of study and of conservation practice by its two authors. It also provides a new appreciation of the specifically Mercian and English political context of its construction. The authors first summarise what is known about the Dyke from archaeology and history and review the debates surrounding its form and purpose. They then set out a systematic approach to understanding the design and construction of the massive linear bank and ditch that has come to stand proxy for the Anglo-Welsh border. What can currently be deduced about the build qualities of the Dyke are then summarised from the authors' recent (and newly intricate) study of details of its localised form and construction and its landscape setting. The authors meanwhile also explain Offa's Dyke as an instrument of late 8th-century Mercian statecraft and the imperial ambitions of Offa himself.