釋氏要覽 1.98

1.98

The history states: "The designation 'head seat' means the elder (sthavira). It is because he occupies the head of the seats and sits above the saṃgha. Emperor Xuānzong of the Tang appointed the monk Bianzhang as Head Seat of the Three Teachings, which was the beginning of this. Nowadays, one is appointed head seat based on learning in scriptures and treatises."