Natyashastra
त्र्यश्रं त्रिकोणं कर्तव्यं नाट्यवेश्मप्रयोक्तृभिः । मध्ये त्रिकोणमेवास्य रङ्गपीठं तु कारयेत् ॥ १०२॥
A triangular (three-sided) structure should be created by the practitioners of the dramatic arts. In the center of this triangular space, the stage (ranga-pitha) should be constructed.
english translation
tryazraM trikoNaM kartavyaM nATyavezmaprayoktRbhiH । madhye trikoNamevAsya raGgapIThaM tu kArayet ॥ 102॥
hk transliteration by Sanscript