Geoffrey Chaucer (1343-1400) is widely considered the greatest English poet of the Middle Ages and was the first poet to have been buried in Poet's Corner of Westminster Abbey. While he achieved fame during his lifetime as an author, philosopher, alchemist and astronomer, composing a scientific treatise on the astrolabe for his son Lewis. Chaucer maintained an active career in the civil service as a bureaucrat, courtier and diplomat. He is best known today for The Canterbury Tales. Chaucer is a crucial figure in developing the legitimacy of the vernacular, Middle English, at a time when the dominant literary languages in England were French and Latin. Chaucer died of unknown causes in1400, but there is no firm evidence for this date, as it comes from the engraving on his tomb, erected more than one hundred years after his death. 75 years after Chaucer's death, The Canterbury Tales was selected by William Caxton to be one of the first books to be printed in England.