  In the context of cyclotomic fields, it is still unknown whether there exist
Euler systems other than the ones derived from cyclotomic units. Nevertheless,
we first give an exposition on how norm-compatible units are generated by any
Euler system, following work of Coates. Then we prove that the units obtained
from Euler systems and the cyclotomic units generate the same
$\mathbb{Z}_{p}$-module for any odd prime $p$. The techniques adopted for the
Iwasawa theoretic proof in latter part of this article originated in Rubin's
work on main conjectures of Iwasawa theory.
