While rightly famous for their roads and aqueducts, how were the Romans at canal digging?
Is there evidence of Roman canals connecting rivers in Europe, or separating Britain from Caledonia (Scotland) north of Hadrian's Wall , or across an isthmus like at Corinth or the Crimea (Bosporan Kingdom)?
Could they have connected the Danube with the Rhine/Main allowing direct shipping from the North Sea to the Black Sea?
This question was probably inspired from the ancient Suez canal discussion, which led me to do a quick search on canal history. A potential problem was they had not invented proper water lock's back then. Since between the two connection points of canals there was a height diffrence, the water would flow strongly in one direction when their water locks were openend, thus allowing only one-way traffic.