Given any system of axioms, there always exist a simpler system in which those axioms can be proved as theorems.
Peano's axioms assert that there exist a set of objects, N, called "natural numbers, and a function s (the "successor function"), from N to N such that
Axiom 1: There exist a unique member of N, call "0", such that s is a one to one function from N to N\{0}.
Axiom 2: If a subset, X, of N contains 0 and, whenever it contains n, it also contains s(n), then X= N.
You can, however, define the natural numbers in terms of sets: 0 is the empty set, 1 is the set containing only 1 (only the empty set), 2 is the set containing only 0 and 1, and, in general, given any n s(n) is the set containing n and all of its members. From that one can show that Peano's axioms are true.
Note: Historically, Peano's axioms included the number 0 as I have here. Nowadays, however, most people start with the number 1.
Werg22, you might find this interesting:
http://academic.gallaudet.edu/courses/MAT/MAT000Ivew.nsf/ID/918f9bc4dda7eb1c8525688700561c74/$file/NUMBERS.pdf