Now we have still to consider inundations. As defensive means and also as phenomena in the natural world they have unquestionably the nearest resemblance to morasses.
They are not common certainly; perhaps Holland is the only country in Europe where they constitute a phenomenon which makes them worth notice in connection with our object; but just that country, on account of the remarkable campaigns of 1672 and 1787, as well as on account of its important relation in itself to both France and Germany, obliges us to devote some consideration to this matter.
The character of these Dutch inundations differs from ordinary swampy and impassable wet low lands in the following respects:
1. The soil itself is dry and consists either of dry meadows or of cultivated fields.
2. For purposes of irrigation or of drainage, a number of small ditches of greater or loss depth and breadth intersect the country in such a way that they may be seen running in lines in parallel directions.
3. Larger canals, inclosed by dykes and intended for irrigation, drainage, and transit of vessels, run through the country in all possible directions and are of such a size that they can only be passed on bridges.
4. The level of the ground throughout the whole district subject to inundation, lies perceptibly under the level of the sea, therefore, of course, under that of the canals.
5. The consequence of this is, that by means of cutting the dams, closing and opening the sluices, the whole country can be laid under water, so that there are no dry roads except on the tops of the dykes, all others being either entirely under water or, at least, so soaked that they become no longer fit for use. Now, if even the inundation is only three or four feet deep, so that, perhaps, for short distances it might be waded through, still even that is made impossible on account of the smaller ditches mentioned under No. 2, which are not visible. It is only where these ditches have a corresponding direction, so that we can move between two of them without crossing either, that the inundation does not constitute in effect an absolute bar to all communication. It is easy to conceive that this exception to the general obstruction can only be for short distances, and, therefore, can only be used for tactical purposes of an entirely special character.
From all this we deduce
1. That the assailant’s means of moving are limited to a more or less small number of practicable lines, which run along very narrow dykes, and usually have a wet ditch on the right and left, consequently form very long defiles.