Kautilya's Arthashastra 7.12.3

7.12.3

tatrāpi sthalanadīparvatadurgāṇām uttarottaraṃ śreyaḥ //

Of forts such as a fort on a plain, in the centre of a river, and on a mountain, that which is mentioned later is of more advantage than the one previously mentioned; of irrigational works (setu-bandha), that which is of perennial water is better than that which is fed wit water drawn from other sources; and of works containing perennial water, that which can irrigate an extensive area is better.