Kautilya's Arthashastra 2.3.11

2.3.11

dvayor aṭṭālakayor madhye saharmyadvitalām adhyardhāyāyāmāṃ pratolīṃ kārayet //

In the intermediate space measuring thirty dandas between two towers, there shall be formed a broad street in two compartments covered over with a roof and two-and- half times as long as it is broad.