  We present simulation results comparing the SU(3) heavy quark potential
extracted from the full Wilson loop expectation to that extracted from the
expectation of the Wilson loop fluctuation solely by elements of Z(3). The two
potentials are found to coincide. This agreement is stable under multiple
smoothings of the configurations which remove short distance fluctuations, and
thus reflects long-distance physics. It strongly indicates that the asymptotic
string tension arises from thick center vortices linking with the Wilson loop.
