What is the link between calligraphy and Zen? Often the Zen books I've read such as Zen Mind Beginners Mind are illustrated by calligraphy oftentimes by the author themselves. Also Zen figures such as the hermit and poet Ryokan are also known for their calligraphy. 

Is there a particular link between Zen and calligraphy? Are the two practice's mutually supportive in some way or is the link purely a matter of both Zen and calligraphy being important in Japanese culture - the link been purely coincidental?
According to the short description of this book calligraphy predated the development of Buddhism in China and Japan. It also says the following about calligraphy:


  "... Calligraphy executed by Zen masters is said to reveal their understanding of the Dharma. It is common practice Zen monks and nuns to learn the art of calligraphy as a part of their monastic training..."


Here you can see some calligraphy letters used in Zen Buddhism and here is a Prezi presentation of Buddhism and Calligraphy. Here is a quote from the presentation:


  "... There are strokes in the characters as there are "eyes" in the sentences of Zen masters. Only those who have the "eyes" can know it. - Huang Tingjian.


Here is a very interesting website on Buddhist Calligraphy in ancient China. In here you will find:


Relationship between Buddhism and Calligraphy
Forms of Buddhist Calligraphy
Calligraphy in Manuscripts
Calligraphy in Inscriptions
Calligraphy and Buddhist Practice


Here is an article on Zen Art. This is a quote from the artiel:


  "... There is a tradition of art practice within Zen. Art arises spontaneously and manifests the buddha-nature within you. Art practice is mindfulness training. The art relies on a foundation of technical training that is then expressed in spontaneous practice. Zen art tends to be simple, sometimes stark, and always lovely ..."


And another quote:


  "... Japanese calligraphy is an art form spiritually expressed through Zen. The artist must be in touch with buddha-nature in order to create an expression of enlightenment. The brush stroke must come from a union with the world; no separation must exist — no I and pen, just the act itself. Japanese calligraphy dates back to the seventh century, where it was part of art practice and meditation in monasteries. Often, the subject of a Japanese calligraphy and painting would be a koan. One of the most common examples of zenga is the open circle, called enso. The simplicity of the enso was particularly popular during the Edo period of Japan in the eighteenth century. Enso symbolized enlightenment, emptiness, and life itself. In the series of ox-herding pictures previously mentioned, the eighth step in the sequence (both ox and self vanish) is represented by enso. During the execution of the calligraphy, the slightest hesitation on the part of the artist will cause the ink to blot on the thin rice paper, and the calligraphy will be ruined. Technique is learned and perfected over many years before such spontaneity is possible. Once the boundary between art supplies, art, and self are gone, the art can be executed ..."


Lanka