Natyashastra
चतुर्भिः सन्निपातैश्च चतुरश्रा प्रमाणतः । आद्यमन्त्यं चतुर्थं च पञ्चमं च तथा गुरु ॥ ११७॥
It is square in shape with four sides, and heavy at the beginning, end, fourth, and fifth.
english translation
caturbhiH sannipAtaizca caturazrA pramANataH । AdyamantyaM caturthaM ca paJcamaM ca tathA guru ॥ 117॥
hk transliteration by Sanscript