 
<translate> Tambayar: Ruwa yana motsa ruwa ta hanyar nauyi kawai, a kan wani ɗan ƙaramin dutse, tubali, ko kuma kankare; da sauri da ruwa yake gudana. Yawancin magudanan ruwa suna ƙarƙashin ƙasa kuma suna bin yanayin ƙasa; ana kauce wa tuddai masu hanawa ko kuma, a wasu lokatai, ana yin rami a ciki. A inda akwai kwari ko ƙasa, ana ɗaukan bututun a kan gada, ko kuma an saka abin da ke ciki a cikin bututun ƙarfe mai ƙarfi, ko kuma a cikin tukwane, ko kuma a cikin dutse. Yawancin tsarin ruwa sun haɗa da tankunan kwari, wanda ya taimaka wajen rage duk wani tarkace da ruwa ke ɗauka. Ruwan ruwa da castella aquae (tankunan rarrabawa) sun tsara wadatarwa zuwa wurare daban-daban. A birane da ƙauyuka, ruwan da ke kwarara daga magudanan ruwa yana zubowa cikin magudanan ruwa da kuma magudanan ruwa.  Amsa wannan tambayar: wane karfi ne Romawa suka yi amfani da shi wajen motsa ruwa? <eng> The question: Aqueducts moved water through gravity alone, along a slight overall downward gradient within conduits of stone, brick, or concrete; the steeper the gradient, the faster the flow. Most conduits were buried beneath the ground and followed the contours of the terrain; obstructing peaks were circumvented or, less often, tunneled through. Where valleys or lowlands intervened, the conduit was carried on bridgework, or its contents fed into high-pressure lead, ceramic, or stone pipes and siphoned across. Most aqueduct systems included sedimentation tanks, which helped reduce any water-borne debris. Sluices and castella aquae (distribution tanks) regulated the supply to individual destinations. In cities and towns, the run-off water from aqueducts scoured the drains and sewers.

Answer this question: what force did the romans use to move water? 