Who led the first voyage to circumnavigate the earth

Ferdinand Megellan ,a portuguese explorer

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

the first forms of writing came from them in the form of pictographs around 3100 bc.