Canvas was originally used for ship sails, tents, sacking and other practical uses. Some other ancient materials that artists used to paint on include painted linen by the Egyptians, painted textiles by pre-Columbian South Americans and painted silk by the Chinese from around 206 B.C.
Western artists started using panels to lay their painted cloths across beginning around the 16th century in Italy and the 17th century in Northern Europe.
According to the J Rank encyclopedia article on Visual Art and Artists, a manuscript (as of April 2010 located in Paris, Bibliothèque Nationale) of 1410 confirms that the English painted on cloth at about this time (early 15th century). After soaking the linen cloth in a loosening gum solution, when the material dried, the artist stretched the cloth out with his hands, laid it flat on a layer of rough wool cloth that absorbed excess moisture, and walked over it with clean feet to keep it stretched.
Andrea Mantegna, a Northern Italian Renaissance painter (1430--1506) noted that canvas could be "wrapped around a rod when being moved," noting a canvas painting's portable nature. Until the 17th century, depictions of artists at work often showed canvases lashed to temporary frames that they would later remove, hanging the canvas as a free-flowing cloth, without the stretchers they used while painting.
Around 1370 to 1440 A.D., artists used linen or silk to create religious processional banners. Artists prepared and painted the canvas cloth on a temporary stretcher.
The stretcher--rounded or cornered pieces of wood stretched to the corners of the frame--allowed a painter to adjust the pictorial space in the image if necessary. This practice gradually developed to become the fixed canvas supports and stretchers seen in the 15th and 16th centuries and today.
As of April 2010, artists can use angled or rounded-edge stretchers. According to artist supply websites and artist experience, stretchers with rounded edges are less damaging to canvas cloth than angled edges.