History of Mathematics
Some primary source material.
Euclid's Elements (c. -300), selections from the beginning and end.
Note his treatment of Eudoxus-style arguments on area versus radius.
Russell and Whitehead's Principia Mathematica (1910),
a selection on the number one.
Check out how formalized the mathematics has become, and compare that with the kinds of statements they
are trying to
prove-- look in particular at the middle of page 362.
Bourbaki's Elements, from the volume on Topology (1940), a selection on
the construction of the reals and
part of the "historical note" .
Here the math should be much more readable, but I mainly just want you to get a sense of their style.