Albrecht Durer (; German: ['albRect 'dy:Ra]; 21 May 1471 - 6 April 1528) was a painter, printmaker, and theorist of the German Renaissance. Born in Nuremberg, Durer established his reputation and influence across Europe when he was still in his twenties due to his high-quality woodcut prints. He was in communication with the major Italian artists of his time, including Raphael, Giovanni Bellini and Leonardo da Vinci, and from 1512 he was patronized by emperor Maximilian I. Durer is commemorated by both the Lutheran and Episcopal Churches.

On his return to Nuremberg, Durer worked on a number of grand projects with religious themes, including a crucifixion scene and a Sacra Conversazione, though neither was completed. This may have been due in part to his declining health, but perhaps also because of the time he gave to the preparation of his theoretical works on geometry and perspective, the proportions of men and horses, and fortification. However, one consequence of this shift in emphasis was that during the last years of his life, Durer produced comparatively little as an artist. In painting, there was only a portrait of Hieronymus Holtzschuher, a Madonna and Child (1526), Salvator Mundi (1526), and two panels showing St. John with St. Peter in background and St. Paul with St. Mark in the background. This last great work, the Four Apostles, was given by Durer to the City of Nuremberg--although he was given 100 guilders in return. As for engravings, Durer's work was restricted to portraits and illustrations for his treatise. The portraits include Cardinal-Elector Albert of Mainz; Frederick the Wise, elector of Saxony; the humanist scholar Willibald Pirckheimer; Philipp Melanchthon, and Erasmus of Rotterdam. For those of the Cardinal, Melanchthon, and Durer's final major work, a drawn portrait of the Nuremberg patrician Ulrich Starck, Durer depicted the sitters in profile, perhaps reflecting a more mathematical approach. Despite complaining of his lack of a formal classical education, Durer was greatly interested in intellectual matters and learned much from his boyhood friend Willibald Pirckheimer, whom he no doubt consulted on the content of many of his images. He also derived great satisfaction from his friendships and correspondence with Erasmus and other scholars. Durer succeeded in producing two books during his lifetime. "The Four Books on Measurement" were published at Nuremberg in 1525 and was the first book for adults on mathematics in German, as well as being cited later by Galileo and Kepler. The other, a work on city fortifications, was published in 1527. "The Four Books on Human Proportion" were published posthumously, shortly after his death in 1528. Durer died in Nuremberg at the age of 56, leaving an estate valued at 6,874 florins -- a considerable sum. He is buried in the Johannisfriedhof cemetery. His large house (purchased in 1509 from the heirs of the astronomer Bernhard Walther), where his workshop was located and where his widow lived until her death in 1539, remains a prominent Nuremberg landmark. It is now a museum. CANNOTANSWERAnswer this question using a quote from the following article:

Why werent they complete?

This may have been due in part to his declining health,