What is "sanseki"

The term Sanseki (三跡) or "three [brush] traces" is used in Japanese to refer to a group of three famous Heian period calligraphers:

• Ono no Michikaze, known as Yaseki from the character 野 in his name.
• Fujiwara no Yukinari, known as Gonseki from 権 in his court title.
• Fujiwara no Sukemasa, known as Saseki from the character 佐 in his name.