The following websites provide useful information when examining the history, doctrines and practices of the Catholic Church.
Overview from Roman Imperial period: Early Christianity
Overview from Charlemagne to the Late Medieval period: Medieval Europe
Church Councils: Major Councils of the Church from DailyCatholic.org
Sacraments: The Seven Sacraments
Monastic Orders: Monastic Overview
Mysticism: Hildegard of Bingen 1098-1179