This paper assesses the alternative models currently proposed for the original design of the Antonine Wall. It argues that there is sufficient evidence of a pattern in the structural relationships between the Wall and its various garrison posts to confirm that there was a major change of plan during the construction process. This resulted in the addition of a series of secondary forts, several of which can now be shown to have replaced primary fortlets, and a concomitant delay in the construction programme. An explanation is offered for this rapid change of design, which resulted in one of the most intensively garrisoned linear frontiers in the Roman Empire.