It has never been discovered precisely how the Byzantine chemists achieve the jet of flame for their 'Greek fire'. It is greeted, and greatly deterred, by a new weapon which can be seen as the precursor of the modern flamethrower. In674 a Muslim fleet enters the Bosphorus to attack Constantinople. Since this is the time of the crusades, it is likely that the idea has been brought from the Middle East. There is a reference to one in France in 1180, and a few years later to another in England. Windmills are first mentioned in Europe in the 12th century. But a first mention of this two centuries after the event makes it unlikely to be true. The date of the first windmill is often given as 644 or earlier, because a 9th-century document says that the man who in that year assassinated the caliph Omar in the mosque at Medina was a Persian builder of windmills. They are descibed in a manuscript by Estakhri, a Persian georgrapher of that period, as having horizontal sails, like the blades of a helicopter, directly linked by a vertical shaft to the millstones turning below. The first practical windmills are constructed in or before the 9th century in a region spanning eastern Iran and western Afghanistan.
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