the first windmills had long vertical shafts with rectangle shaped blades. they existed in persia in the 9th century. there is a story about a windmill and the second caliph umar (634\644 ad). it is not known if this is a true story. these windmills were made of six to twelve sails. the sails were covered in reed matting or cloth. they were very different from european versions. a similar type of vertical shaft windmill with rectangle blades can also be found in 13th century china. they were used for irrigation.