The engineering skill needed to cope with this situation was very great; and if proof be required that the Romans exercised it, the answer is sufficient that neither before nor for a thousand years after this period was there a central organisation strong enough to carry out such operations. The work had to be of two kinds—draining, to carry off the flood-water and void the rainfall coming from the high land, and embanking, to shut out the sea. In the former the Romans acted upon sound principles, which were often neglected in after times. They used the natural rivers as arterial drains, and led the subsidiary drains into them. History records that they executed similar works in other parts of the Empire. The Pontine marshes and the Lombard valley of the Po were drained under the Republic. The Emperors Claudius and Hadrian began and completed a canal between the Fucine Lake and the Liris. In the Low Countries, Drusus, in 12 B.C., drew a channel connecting Lake Flevo (Zuyder Zee) and the Rhine; and in A.D. 47 Corbulo made a canal, twenty-three miles in length, between the Rhine and the Meuse. Eleven years later a project for uniting the Saone and the Moselle, and thus completing a waterway from the Mediterranean to the North Sea, was only not attempted from fear of the jealousy of Nero. If a full account was ever written of the Roman settlement of Britain, the operations now to be described must have filled a large place in it. The present channel of the Witham from Lincoln to Boston is much too straight to have ever been the course of a natural stream. From Chapel Hill just below Dogdyke, where there was a tidal creek, the river was canalised to Boston as late as 1761; but there is no record in historical times of such an operation in the twenty miles from Lincoln to Dogdyke. In order to drain the lower mere described above, a channel was cut along the high land for that distance, and the upper waters of the river directed into it. In very early (perhaps in Roman) times there was another branch of the Witham due east from Dogdyke through the upper fen to Wainfleet, where it received the Steeping, and thence into the sea near Gibraltar Point. Very probably it was the draining of the district near Lincoln which hastened the silting up of this ancient channel. But at no time can it have been, as some have fancied,[20] the principal outfall of the river, for it is much farther from the sea, and could not have been tidal, like the other, for the whole distance.