Dutch ships attacking Damiate during the Fifth Crusade. Window in the church of St John (Gouda).

Dutch ships attacking Damietta during the Fifth Crusade. Window in the church of St John (Gouda).

Meanwhile, the ground continued to subside. This would inevitably have led to more flooding in the fifteenth century if it had not been for one amazing invention in 1408: the polder mill. That you could use wind energy to grind corn was one of the things the Crusaders had learnt from the Arabs in the twelfth century. Very soon every medieval city had a corn mill built into the city walls. However, the idea of driving the sails by means of a wheel and rotor was completely new. In this way it was possible to pump water upwards which would ensure that the polders of Holland would never again be swamped.

The first polder mills were built at Alkmaar in 1408 on the initiative of two private individuals. When the Count received an enthusiastic report about this innovation, he requested the water boards to visit Alkmaar as soon as possible. That same year a second polder mill was built at Leiden and after that many more followed. Because construction costs were high, many water boards were reluctant to acquire polder mills. The provincial government did everything possible to persuade the boards to invest in the mills but there was never a question of the Count ordering them to do so. This makes it again abundantly clear that it was not a command economy, but one based on consultation.

When he stimulated the construction of polder mills, the Count was thinking of his own coffers more than anything else. The peasant farmers were taxpayers and the more they increased production, the more the Count’s income from taxes increased. The suggestion to build mills was therefore, first and foremost, a question of enlightened self-interest. Yet it had far wider consequences.

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