Hypothetically speaking, lets say a Roman general set out from the city of Rome with an army of 10,000 men. Assuming ships were prepared ahead of time for when the army reached the sea, about how long total would it take to transport this army from Rome to the Island of Great Britain? This includes the march, sea voyage, rest, eating, etc. Total time. Thanks
From Rome to Gesoriacum, the port at Boulogne-sur-Mer, with two legions, at normal marching speed, overland, is about 60 days, covering about 1700km. With a few stretches of forced marches, you could cut that down to about 50 days. This route goes north from Rome via Arretium and then across to the Po Valley, then westward down the valley via Mutina-Placentia-Vercellae and across the Alps at Augusta Praetoria. Once in Gaul, the route veers north to Augusta Raurica and then west across central Gaul to Samarobriga, just north of Lutetia (Paris), and then to Gesoriacum.
From Gesoriacum, assuming all transport is waiting, and assuming it is Summer and good weather, it is only 2-3 days to Londinium, about 3 days to Camulodunum (Colchester), and about 5 days to Eburacum (York).