36 or city walls. In addition, the water can neither be too shallow nor too deep, since the former would not provide enough obstruction for troops, their cavalry and their wheeled artillery; while the latter would allow boats to transfer the enemy across the waterline.Aside from making it very difficult to cross the water, an ideal depth of about 40 centimetres would also hide any indications of trenches, elevated roads and other variations in the landscape that make it easy to misstep.9 Another inconvenience for the Dutch that was welcomed by the French were several remarkably severe winters, causing the waterline to freeze to such an extent that the French could simply walk across it. When this happened, the Dutch did what they do best: ice skating, in this case with weaponss to attack the enemy. When the rivers froze, orders were given to manually break the ice so that the waterline could maintain its purpose.10 This had been a problem during the war against Spain and it continued to be an issue for at least another century. When this war against the French ended, the Dutch decided to upgrade the waterline, because of the French successes in crossing it on some occasions. When they did, the villages and mills were usually burnt to the ground, so the agricultural land of the farmers had been severely damaged by the water but the waterline could not be drained without mills.11 Additional damage was done in the northern parts of the waterline that had not been flooded by the rivers but by the Zuiderzee, carrying salt water into the provinces. It took over seventy years to restore and refine the waterline before it would serve the Dutch only one more time. The waterline was made ready for defence in both the Austrian and the Spanish succession wars but was not used in either occasion. It was used just one more time when Prussian army attacked the Republic in 1787, but because of the sudden advance of the troops, there was not enough time to fully prepare the waterline and the Prussians had no trouble breaking through.12 After the construction of the Nieuwe Hollandse Waterlinie, some vestingen (bastions) were torn down and transformed into the first recreational sites because they were no longer necessary for defensive purposes.13 The Nieuwe Hollandse Waterlinie Plans for a second waterline came in 1811, after many renovations were considered and some of these executed for the old waterline. These plans dated back to those of 1629, which the Republic could not coordinate and afford during the war. At first, the construction of a new waterline that would include the city of Utrecht (that had been
conquered by the French in 1673) appeared too expensive, but during the rule of Napoleon in the Netherlands, some engineers were ordered to make designs for a defensive system that would also protect the more eastern parts of the province of Utrecht. Just like the realization of the existing Hollandse Waterlinie, the plans for the project of building a new waterline were not executed for another few years. However, this time it was not the attack of an enemy that incited the construction of the waterline, but the progressive mindset of the first king of the Kingdom of the Netherlands, Willem I. The construction began in 1815 without the pressure experienced in 1629.14 Because more time was available and almost two centuries had past, the new waterline was technologically more advanced than the previous one. For example, the new waterline was constructed in five sections, called kommen (bowls), which could be inundated apart from each other, separated by special inundation sluices strong enough to open in the high water levels of rivers, canals and lakes. These measures made sure that land would only be flooded where it was intended. The transportation routes that crossed the line were altered so that they too could be easily sealed in times of war. The waterline was also enforced by new ´tower fortresses´ that could withstand gunpowder-based artillery and cannons.15 What had been used for the construction of the Oude Hollandse Waterlinie but was considered even more for the new one, was all sorts of vegetation.They had been sporadically applied to the previous waterline, but in the new waterline, plants such as thorny hedges were part of the blueprints of the fortresses. Breeding sites for particular species of trees and plants were created to supply the vegetation for both the fortresses in construction as the old ones being updated. It was at first mainly used as obstacle and a source of wood near the fortresses, but later is was also employed to camouflage the fortresses, its men and its artillery. On the roads near the fortresses, vegetation was used to block the path.16