Those gardens were laid out in the 18th century by Jacques-Philip Maréschal, engineer of Nîmes fortifications. They are located bottom of mount Cavalier, where the tower Magne stands.
All the ponds (including the canal created in 1750) are supplied by the famous Nemausus source: well, Nîmes city was founded upon this fountain... They discovered a huge Gallo-Roman complex (thermae, houses), when the first landscapings took place.
That's as may be, but those formal gardens are gorgeous: come here one second, near the quivering water, sit here and enjoy the warm Provençal sun! You can see beautiful statues, vast lawns, huge trees... You know what? Those gardens were the first public park created in Europe!