preparations for dealing with Carausius, Diocletian returned from the East. The emperors met that year, but neither date nor place is known with certainty. They probably agreed on a joint campaign against the Alamanni and a naval expedition against Carausius. Later in the year, Maximian led a surprise invasion of the Agri Decumates – a region between the upper Rhine and upper Danube deep within Alamanni territory – while Diocletian invaded Germany via Raetia. Both emperors burned crops and food supplies as they went, destroying the Germans' means of sustenance. They added large swathes of territory to the Empire and allowed Maximian's build-up to proceed without further disturbance. In the aftermath of the war, towns along the Rhine were rebuilt, bridgeheads created on the eastern banks at such places as Mainz and Cologne, and a military frontier was established, comprising forts, roads, and fortified towns. A military highway through Tornacum (Tournai, Belgium), Bavacum (Bavay, France), Atuatuca Tungrorum (Tongeren, Belgium), Mosae Trajectum (Maastricht, Netherlands), and Cologne connected points along the frontier. Constantius, Gennobaudes, and resettlement In early 288, Maximian appointed his praetorian prefect Constantius Chlorus, husband of Maximian's daughter Theodora, to lead a campaign against Carausius' Frankish allies. These Franks controlled the Rhine estuaries, thwarting sea-attacks against Carausius. Constantius moved north through their territory, wreaking havoc, and reaching the North Sea. The Franks sued for peace and in the subsequent settlement Maximian reinstated the deposed Frankish king Gennobaudes. Gennobaudes became Maximian's vassal and, with lesser Frankish chiefs in turn swearing loyalty to Gennobaudes, Roman regional dominance was assured. Maximian allowed a settlement of Frisii, Salian Franks, Chamavi and other tribes along a strip of Roman territory, either between the Rhine and Waal rivers from Noviomagus (Nijmegen, Netherlands) to Traiectum, (Utrecht, Netherlands) or near Trier. These tribes were allowed to settle on the condition that they acknowledged Roman dominance. Their presence provided a ready pool of manpower and prevented the settlement of other Frankish tribes, giving Maximian a buffer along the northern Rhine and reducing his need to garrison the region. Later campaigns in Britain and Gaul Failed expedition against Carausius By 289, Maximian was prepared to invade Carausius' Britain, but for some reason the plan failed. Maximian's panegyrist of 289 was optimistic about the campaign's prospects, but the panegyrist of 291 made no mention of it. Constantius' panegyrist suggested that his fleet was lost to a storm, but this might simply