In the summer of 1248, Albertus was sent to Cologne to organize the first Dominican studium generale (“general house of studies”) in Germany. He presided over the house until 1254 and devoted himself to a full schedule of studying, teaching, and writing. During this period his chief disciple, Thomas Aquinas, returned to Paris in 1252 and the two men maintained a close relationship. From 1254 to 1257 Albertus was provincial of “Teutonia,” the German province of the Dominicans. Although burdened with added administrative duties, he continued his writing and scientific observation and research.
Albertus resigned the office of provincial in 1257 and resumed teaching in Cologne. In 1259 he was appointed by the pope to succeed the bishop of Regensburg, and he was installed as bishop in January 1260. After Alexander IV died in 1261, Albertus was able to resign his episcopal see and return to his order and teaching in Cologne. From 1263 to 1264 he was legate of Pope Urban IV, preaching the crusade throughout Germany and Bohemia; subsequently, he lectured at Würzburg and at Strasbourg. In 1270 he settled definitively at Cologne, where, as he had done in 1252 and in 1258, he made peace between the archbishop and his city.
During his final years he made two long journeys from Cologne. In 1274 he attended the second Council of Lyon, France, and spoke in favor of acknowledging Rudolf of Habsburg as German king. In 1277 he traveled to Paris to uphold the recently condemned good name and writings of Thomas Aquinas, who had died a few years before, and to defend certain Aristotelian doctrines that both he and Thomas held to be true.
Albertus’ works represent the entire body of European knowledge of his time not only in theology but also in philosophy and the natural sciences. His importance for medieval science essentially consists in his bringing Aristotelianism to the fore against reactionary tendencies in contemporary theology. On the other hand, without feeling any discrepancy in it, he also gave the widest latitude to Neoplatonic speculation, which was continued by Ulrich of Strasbourg and by the German mystics of the 14th century. It was by his writings on the natural sciences, however, that he exercised the greatest influence. Albertus must be regarded as unique in his time for having made accessible and available the Aristotelian knowledge of nature and for having enriched it by his own observations in all branches of the natural sciences. A preeminent place in the history of science is accorded to him because of this achievement.