Albertus was a Dominican monk and the most eminent naturalist of the 13th century; his work on animals contained a good deal of personal observation. He was the first to comment on virtually all of the writings of Aristotle, thus making them accessible to wider academic debate. The study of Aristotle also brought him to study and comment on the teachings of Muslim academics, notably Avicenna and Averroes. It has been said that most modern knowledge of Aristotle was preserved and presented by Albertus. The influence of his writings, many of which were theological, is attested by the fact that there were 300 printed editions of different works by him published in the 15th century. The edition of 1478 is the earliest cited by the ISTC (No. ia00223000).