the three famous ancient calligraphers (Emperor Saga, Tachibana (no) Hayanari and Kooboo Daishi)
三筆の一人である空海は書の達人だった。
Kūkai, one of the Three Brushes, was a master of calligraphy.
三筆の書を展覧会で鑑賞した。
I appreciated the calligraphy of the Three Brushes at the exhibition.
三筆の名は書道史に永遠に刻まれている。
The names of the Three Brushes are forever engraved in the history of calligraphy.