Windmolen — The MSX Tower Defense Game Before Tower Defense Existed
Years before Desktop Tower Defense or Plants vs. Zombies, a water engineering student in Wageningen was building a game with remarkably similar mechanics — except instead of defending against invading enemies, you were defending against water. Windmolen (“Windmill”), released in 1989 for the MSX2, may be the earliest example of what we now call tower defense gameplay.
The Game
The concept was elegantly Dutch. You’re in charge of a polder — a low-lying area of land reclaimed from the sea, kept dry by a system of dikes and drainage windmills. Water constantly seeps in through the soil, rises in the ditches, and threatens to flood your farmland. Your job: place windmills to pump the water out.
Each level presents a map divided into tiles. Water enters from designated points — canal gates, dike breaches, and rainfall. It flows across the terrain following topography, pooling in low areas. Windmills, when placed adjacent to waterways, actively pump water from one tile to the next, eventually moving it off the edge of the map into the sea.
The strategic depth came from windmill types. The basic wipmolen (post mill) was cheap but slow. The bovenkruier (smock mill) pumped faster but cost three times as much. The expensive stoomgemaal (steam pumping station) was devastatingly effective but required fuel deliveries from a supply depot. Players earned guilders based on how much farmland remained dry at the end of each round.
Later levels introduced complications: the wind would change direction (affecting windmill efficiency), dikes would develop leaks requiring immediate sandbagging, and certain tiles contained peat that could collapse if the water table dropped too far — a historically accurate detail that only a water engineering student would think to include.
The Developer
Bas Vermeer was in his second year of water engineering (waterbouwkunde) at Wageningen University when he created Windmolen. The game was directly inspired by his coursework.
“We’d just finished a module on historical water management in the Netherlands,” Vermeer explained via email. “I was fascinated by how the old windmill systems worked — how you needed chains of mills to lift water from the deep polders up to sea level. And I thought, there’s a game in this.”
Vermeer wrote the game in MSX-BASIC with critical routines in Z80 assembly. The water flow simulation — the most technically demanding part — used a simplified cellular automaton model. Each tile had a water level value, and on each game tick, water would flow from high-level tiles to adjacent low-level tiles. Windmills reversed this flow in their radius of effect.
“Getting the water to look right was the hardest part,” Vermeer said. “I used different shades of blue in the MSX2 palette to show water depth. When a field started flooding, you’d see it gradually turn from green to light blue to dark blue. That visual feedback was important — you needed to see where the trouble was coming from.”
Development took about five months, mostly during evenings when Vermeer should have been studying.
Release
Vermeer sold Windmolen on 3.5-inch floppy disk, advertised through MSX Computer Magazine and distributed at MSX user group meetings in Wageningen and Arnhem. Copies were priced at ƒ19.95. About 90 were sold.
The game received a brief mention in MSX Computer Magazine, which praised its originality but noted the slow pace: “You need patience — this is not an action game. But if you’ve ever wondered how the Netherlands stays dry, this is your game.”
Legacy
Vermeer completed his degree and went on to work at Rijkswaterstaat (the Dutch national water authority), where he spent his career working on flood management systems. He finds the parallel amusing.
“I went from simulating water management on an MSX to doing it for real,” he said. “The principles are surprisingly similar — it’s all about where you place your pumping capacity and how you handle peak flows. The MSX version was just a lot less paperwork.”
When we described the modern tower defense genre to Vermeer, he was intrigued. “So people are placing towers along a path to stop enemies from reaching a goal? That is exactly what Windmolen does — except the enemy is water and the towers are windmills. I suppose great minds think alike.”
The game has been preserved as a ROM image and runs in openMSX. Its water simulation remains surprisingly compelling — watching the blue creep across your carefully managed polder while you scramble to place windmills is exactly the kind of satisfying panic that makes tower defense games addictive.
See also: Kabeljauw — another lost Dutch MSX game from the late 1980s, and Dijkbreker — a game with a similar “fighting the water” theme on the Amstrad CPC.