Bassin de Neptune
You are at the Pool of Neptune. Slowly walk around it, keeping the water to your right. Motifs from the sea are found all about, including lobsters, walrus, narwahls, fish, crabs, sea turtles, and fantasy monsters of the deep. Neptune is the central figure holding his trident aloft, and his wife Salacia, goddess of salt, sits to the right, holding a triton, a sort of merman or cherub of the sea. Lesser gods help Neptune control all bodies of water and sea life. Ocean to his right rides a sea unicorn, and Proteus to his left, who is the old man of the sea we saw before at Apollo's basin, has tamed a giant squid.
This Pool is the grandest in the gardens, and the scene of their most spectacular water works, with 99 jets shooting to make patterns in the air and on the surface. On Summer nights, they synchronise with a soundtrack and light show, sometimes projecting holograms onto a wall of spray.
Visitors in Louis XIV's time marvelled at the craftsmanship and wondered at the science involved in bringing the water here. Fully one third of the budget allocated to Versailles was spent on water engineering. You must remember that at the inauguration, the gardens contained more than double the number of fountains that you see today. At the time, the gardens consumed more water per day than the entire city of Paris!
Both the first and second plans for the water works were insufficient to run all the fountains at once. They were turned on in succession as the king and his entourage approached, and quickly stopped once the throng passed. This did not suit the king at all, and he ordered the most cartesian minds in the kingdom to meet and solve the problem.
A project was concocted that appeared far-fetched. Water would be brought from the Seine, which was only 10km away. However, Versailles being more than 150 meters above the level of the river at the nearest point, Marly, water would have to climb nearly all those meters right at the start, on the hill that bordered the Seine. A massive pump, the likes of which the world had never seen, would need to be constructed to push that voluminous mass of water uphill. The behemoth was called the "Machine of Marly."
The king gave carte blanche to the project, which also included an aqueduct running through Louveciennes. The infernal din from the 14 massive wheels of the machine, running 24/7 made it impossible to live within proximity, and it could even be heard more than 5km away in Fourqueux.
The Machine of Marly was supposed to produce the required 6000 cubic meters of water per day, which would have kept all fountains running constantly. However, due to immense pressure on the Machine and breakdowns from the mostly wooden parts, it never operated at more than 80% of capacity, and deteriorated quickly over time to 50%.
Rather than settle for that level of productivity, which could easily be stocked and power the biggest water display in Europe for several hours straight, the king engaged an even more ambitious plan. The Eure river is 27 meters above Versailles, but lies 80km away. A massive canal would need to snake across the land, including an aqueduct 18km long, never allowing the water to fall more than 33cm per km, that's about a foot per mile. In a brief period of peacetime, the king set 20000 soldiers on diverting the water. After several years on the job, war broke out and work was stopped. It never resumed, due to the collosal costs. More than 10000 workers died on the project, and all that's left are the vestiges of a half-built aqueduct at the castle of Maintenon.
Luckily, today's electric pumps send 10000 cubic meters of water per hour to Versailles and 22 surrounding communities. Amazingly, what the engineers made on the garden grounds 350 years ago is still used to run the fountains today: all the pipes, the spigots, even the meter-high U-shaped wrenches twisted to turn on and off the flow, are the originals.
When you've completed your tour of Neptune, walk straight ahead to the leftmost entrance of the wood before you.