VIKINGS WARRIORS AND TRADERS

Ludwig continues Charlemagne's defensive work in Friesland, Caligula's old lantern is restored as part of the defenses. Spain: Count Bera rejects an attack by the Emir of Cordoba on Barcelona, belonging to the Franks. Abd al-Karim ibn Mugait attacks and conquers several Christian villages on the banks of the Naharon River, but the approach of a Christian army and torrential rains force him to abandon the campaign. Synod of Constantinople: Leo V forbids the cult of images confirms the iconoclastic theses and banishes Nicéphore, patriarch of Constantinople, naming Theodotus in his place. Al-Mamun brings the Abbasid Caliphate to its cultural peak, the alchemist Yabir discovers sulphuric and nitric acids, separates arsenic and antimony from sulphides and writes the treatise on chemistry Summa Perfectionis, and the mathematician Al-Jwarizm, from whose name the terms guarism and algorithm are derived, writes the Book of Reduction (Kitab al-Yabr: algebra) with the first algebraic slide rules.