Theodorus Moretus, also known as Theodor or Theodore Moretus (1602–1667) was a Flemish Jesuit priest who was also a mathematician, geometer, theologian and philosopher. He spent most of his working life in Prague and Breslau (now Wroclaw) where he taught philosophy, theology and mathematics. He published a number of treatises on these three subjects and also on physics and music theory. Life Theodorus Moretus was born in Antwerp, the son of Pieter Moretus and Henrica Plantin. Both his parents were from prominent printing families: his mother was a daughter of Christophe Plantin, the founder of the famous Plantin Press in Antwerp while his father was the brother of Jan Moretus who was initially an assistant of Plantin, married another Plantin daughter and, after taking over the Plantin Press from his father-in-law, steered the business to further success well into the 17th century. Theodorus Moretus' father was a diamond trader and cutter. Moretus studied mathematics at the Jesuit school in Antwerp founded by François d'Aguilon. He was a student at this school for seven years. He joined the Jesuit order in Mechelen as a novice on 15 November 1618. He then studied at the University of Leuven. He took physics in 1622–1623 and studied theology from 1623 to 1627. In 1627–28 Moretus is mentioned as a teacher of syntax in Bruges. His title was Magister, which indicates he had not been formally ordained yet. His aptitude for science (particularly mathematics) was appreciated early on by Father Gregorius van St-Vincent, who had arranged for Moretus to be able to continue his studies in Louvain without first having to spend a few years in colleges. Gregorius van Vincent also arranged for Moretus to send dissertations on mathematical subjects to Christoph Grienberger, the chair of mathematics at the Collegio Romano in Rome who reviewed them. Moretus was possibly ordained as a priest in 1628–29. In 1629–30 Moretus was teaching in Münster. The next year he moved to Prague to join Gregorius van Vincent who had been sent there to teach mathematics. Moretus was to assist the ailing Gregorius in his teaching duties. The following year, the invasion of the Swedes and the sacking of Prague during the Thirty Years' War forced both to leave Prague. While van Vincent first went to Vienna to recover, Moretus was sent to Olomouc (now in the Czech Republic), where he taught philosophy and other subjects until 1634. By