384 irrigation
at the court of Countess Matilda of TUSCANY(1046–
1111) and later for the emperors Henry V (r. 1111–25)
and Lothair III (r. 1133–37). He was considered one of
the founders of the law school and of the University of
Bologna. He died about 1130.
See alsoGRATIAN; LAW, CANON AND ECCLESIASTICAL.
Further reading:Herman Kantorowicz, Studies in the
Glossators of the Roman Law: Newly Discovered Writings of
the 12th Century,ed. William Warwick Buckland (1938;
reprint, Aalen: Scientia, 1969), 33–37; Hastings Randall,
The Universities of Europe in the Middle Ages,3 vols., ed. F.
M. Powicke and A. B. Emden (1895; reprint, Oxford:
Clarendon Press, 1936); Richard Southern, Scholastic
Humanism and the Unification of Europe,Vol. 1, Founda-
tions(Oxford: Blackwell, 1995).
irrigation Irrigation was practiced by medieval ARABand
by LATINfarmers who needed to adopt that style of AGRI-
CULTUREbecause of the introduction of new crops from the
East, whose climate was characterized by a monsoon sea-
son of heavy rain. These were sugarcane, rice, cotton,
watermelon, and oranges, all of which could not be grown
without irrigation. The introduction of these crops growing
in the summer stimulated the development of rotation with
crops that could grow in the winter. But all required contin-
uous cultivation and large quantities of water.
The Romans had adopted water-lifting devices from
the arid Near East and built aqueducts still used in the
Middle Ages. Most irrigation around the medieval Mediter-
ranean was by gravity flow from continuous or intermit-
tent streams. The Arabs supplement the old gravity-flow
irrigation with the use of a wheel powered by moving
water or of animals to raise water with buckets or a chain
of pots. This device enabled single families, primarily in
Arab dominated regions, to produce an agricultural sur-
plus for the families and for the new cities from continu-
ously cultivated land. Disputes over water distribution
were constant everywhere in courts and frequent subjects
in legal codes, though most were resolved locally. Water
was mostly viewed as a common or public resource and
was not controlled by lords and ecclesiastical institutions.
See alsoAGRICULTURES; MILLS, WATER AND WIND.
Further reading: Thomas F. Glick, Irrigation and
Society in Medieval Valencia(Cambridge: Belknap Press of
Harvard University Press, 1970); Thomas F. Glick, Irriga-
tion and Hydraulic Technology: Medieval Spain and Its
Legacy(Aldershot: Variorum, 1996); Andrew M. Watson,
Agricultural Innovation in the Early Islamic World: The Dif-
fusion of Crops and Farming Techniques, 700–1100(Cam-
bridge: Cambridge University Press, 1983).
Isaac I Komnenos (Comnenus) (ca. 1005–1061)
reforming Byzantine emperor
Isaac was born about 1005/06. After his overthrow of
Emperor Michael VI (r. 1056–57) in 1057, his brief reign
seemed to promise a restoration of Byzantium’s military
power. His reforms alienated the civil bureaucracy, whose
incomes from pensions and salaries were cut drastically.
In addition, new tax surcharges on the provinces and the
collection of unpaid taxes did not make him popular. The
patriarch Michael I Keroularios (r. 1043–58) turned
against him when he revived the antimonastic legislation
of the emperor Nikephoros II Phokas (r. 963–969) and
appointed Michael PSELLOSas his chief minister. Isaac
removed Keroularios and appointed Constantine III Lei-
choudes (r. 1059–63) in his place, alienating his follow-
ers within the church. Threats from Petchenegs and
Hungarians were beaten back. Isaac became increasingly
isolated, and when he fell ill in 1059 Psellos persuaded
him to retire to a monastery, where he died in 1061.
Further reading:Michael Psellos, Fourteen Byzantine
Rulers: The Chronographia of Michael Psellus,trans. E.R.A.
Sewter (Baltimore: Penguin Books, 1953), 275–331; A. P.
Kazhdan and Ann Wharton Epstein, Change in Byzantine
Culture in the Eleventh and Twelfth Centuries(Berkeley:
University of California Press, 1985); George Ostro-
gorsky, History of the Byzantine State,trans. Joan Hussey
(Oxford: Basil Blackwell, 1956); Warren Treadgold, A
History of the Byzantine State and Society(Stanford, Calif.:
Stanford University Press, 1997).Isaac II Angelos(1155–1204) Byzantine emperor
Born about 1155, Isaac was related to the Komnenoi fam-
ily. He was proclaimed emperor after the death of
Andronikos I (r. 1183–85) in 1185. His general Alexios
Branas (d. 1187) repulsed WILLIAM II’s invasion from
Italy in 1185. From then on his reign can be best charac-
terized by decline. In 1187, while he peddled state offices
to renovate the Great Palace, Alexios Branas revolted but
was soon defeated by Conrad of Montferrat, Isaac’s new
brother-in-law. In that same year an expedition failed to
recover CYPRUSfrom the rebel ISAACI KOMNENOS. The
VLACHSand Bulgarians revolted under Peter of Bulgaria
and Asen I (r. 1187–96). In 1190 Isaac II vainly resisted
the passage of FREDERICKI BARBAROSSAduring the Third
CRUSADEbecause of his agreement with SALADIN. Freder-
ick I’s successful occupation of ADRIANOPLElater forced
Isaac to adopt neutrality by 1190. In 1195 Isaac was over-
thrown and blinded by his brother, Alexios III (r.
1195–1203). Eight years later he was replaced briefly on
the throne by his son, Alexios IV (r. 1203–04), only to be
overthrown the following year by Alexios V (r. 1204). He
died in late January of 1204 just before the sack of CON-
STANTINOPLEby the crusaders and Venetians.
See also DANDOLO, ENRICO, DOGE OFVENICE; VILLE-
HARDOUIN, GEOFFROI DE.
Further reading: Niketas Chroniate ̄s, O City of
Byzantium: Annals of Niketas Chroniate ̄s,trans. Harry J.
Magoulias (Detroit: Wayne State University Press, 1984),
197–248, 301–309; A. P. Kazhdan and Ann Wharton
Epstein, Change in Byzantine Culture in the Eleventh
and Twelfth Centuries(Berkeley: University of California