در جمله زیرThe roads in the avenue had been watered به چه معناست؟

Passing through a gateway, we entered a beautiful avenue of plane-trees, planted in four rows. On each side were lofty walls, in  which were arches of open brick-work: on the other side of the walls were gardens. The roads in the avenue had been watered, and there were basins and tanks of water at intervals.