The Plague Years of 1665 and 1666
In 1666, when Cambridge University had been closed due to the Great Plague, one Isaac Newton retired to Woolsthorpe, and over a period of two years developed theories in optics, gravity and early calculus (“the method of fluxions and fluents…“):
All this was in the two plague years of 1665 & 1666. For in those days I was in the prime of my age for invention & minded Mathematicks & Philosophy more then at any time since … 
: Whiteside, D. T. “Newton’s Marvellous Year: 1666 and All That.” Notes and Records of the Royal Society of London 21, no. 1 (1966): 32-41. Accessed April 17, 2020. JSTOR 530816.
: Newton’s Waste Book (MS Add.4004), fols 57r-57v