Valmiki Ramayana Yuddha Kanda Sarga 3 Shloka 16

द्वारेषु: at the entrance of gateways,चत्वार: on four sides, परमायताः very extensive, बहुभिः huge, यन्त्रै: engines, महद्भि: huge,गृहपङ्क्तिभिः rows of houses, उपेताः when people approach, तासां: movable bridges, सङ्क्रमाः four roadways

At the entrance of the gateways around the moats are four road ways. Huge engines are fixed to move the bridges when people approach. There are rows of houses (for the guards) at the gateways.