In the summer of a.d. 122, Hadrian (a.d. 117–38) visited Britain as part of his first major journey. It is broadly accepted that the construction of Hadrian's Wall was inaugurated on this occasion. Following recent advances in Upper Germany where the limes palisade is now known to have been under construction when Hadrian visited the province, this paper re-examines the various strands of evidence for the early chronology of the Wall. It is argued that work started well before a.d. 122 and that it was in fact the ‘fort decision’ which resulted from the imperial visit. The revised sequence offers a fresh perspective on several classic Wall problems and prepares the ground for a new understanding of unique features like the milecastles and Vallum.