"Rigor and Proof in Mathematics: A Historical Perspective" by Israel Kleiner. Mathematics Magazine December 1991, 64:291-314.

This paper gives a very nice overview of how the understanding of rigor in mathematics has evolved from the early ages to the 20th century. 

[https://www.jstor.org/stable/2690647][1]


  [1]: https://www.jstor.org/stable/2690647