Empress

An empress (imperatrix in Latin) is a female emperor, or monarch ruling over an empire. Like queens regnant, empresses in medieval history ruled by their own right, though some ruled jointly, such as Zoe and Theodora of the Byzantine Empire.

List of medieval empresses
The following is a (possibly incomplete) list of known empresses from medieval history.

Byzantine Empire

 * Irene of Athens (reigned 797–802) was consort to the emperor Leo IV from 775-780, then empress dowager during her son Constantine VI's reign after her husband's death in 780. In 797, Irene acceded to the throne as empress regnant and ruled for five years until she was deposed and exiled in 802.
 * Zoe (reigned 1028-1041 and 1042-1050) ruled with her consorts Romanos III and Michael IV from 1028-1041, and ruled jointly with her third husband Constantine IX and her sister Theodora from 1042-1050.
 * Theodora (reigned 1042–1056) ruled from 1042 jointly with her sister Zoe and her third husband Constantine IX, and from 1055 until her death reigned as sole monarch over the empire.