What had a major influence on the development of calligraphy during the Heian period?

In the Heian period, a style of calligraphy emerged that was unique to Japan. Writing had been popularized and the kana syllabarywas devised to deal with elements of pronunciation that could not be written with the borrowed Chinese characters. At the time, Japanese calligraphers still fitted the basic characters, called kanji (漢), into the squares laid out centuries before. Soukou Shujitsu is regarded to be the first text that shows a style unique to Japanese calligraphy. This Tanka (短) poem was written in 749 CE and shows some differences from Chinese calligraphy. The authentically

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