Traditionally, the beginning of this period is set on the date Ras Mikael Sehul deposed Emperor Iyoas I (7 May 1769), and its end to Kassa's coronation as Emperor Tewodros II (11 February 1855), having defeated in battle all of his rivals. Some historians date the murder of Iyasu I (Iyasu the Great) (13 October 1706), and the resultant decline in the prestige of the dynasty, as the beginning of this period. Others date it to the beginning of Iyoas's reign (26 June 1755).