The Canal of Drusus is mentioned by Suetonius (Claudius, 1) and Tacitus (Annals, II.8); it appears that it was dug when the Roman general Drusus campaigned east and north of the Rhine in 12-9 BCE. There have been several theories about its location, one of them being that it is identical to the river Vecht, another stressing that both Suetonius and Tacitus use a plural, and that a second canal had to exist, which was localised between Lake Flevo (the modern IJsselmeer) and the Wadden Sea.
The consensus, however, was that the Canal of Drusus connected the Rhine to the IJssel, and was identical to the water course between modern Arnhem and Doesburg, now called Gelderse IJssel. The main argument was that a monument known as Drusus’ Mole can be found a bit east of this watercourse, at Herwen (ancient Carvium).
This hypothesis now turns out to be incorrect. In a recent article in the Netherlands Journal of Geosciences 87/4 (2008 ) by B. Makaske, G.J. Maas & D.G. van Smeerdijk, “The age and origin of the Gelderse IJssel“, radiocarbon data are mentioned that date the oldest part of the Gelderse IJssel to the tenth century. Of course, it remains possible that the Canal was between Arnhem and Doesburg, later changed its course, and that the samples were taken from this new meander.