  We report on the observation of the hysteretic transition of a commensurate
charge modulation in IrTe$_2$ from transport and scanning tunneling microscopy
(STM) studies. Below the transition ($T_{\rm C} \approx 275$ K on cooling) a $q
= 1/5$ charge modulation was observed, which is consistent with previous
studies. Additional modulations [$q_n = (3n+2)^{-1}$] appear below a second
transition at $T_{\rm S}\approx 180$ K on cooling. The coexistence of various
modulations persist up to $T_{\rm C}$ on warming. The atomic structures of
charge modulations and the temperature dependent STM studies suggest that 1/5
modulation is a periodic soliton lattice which partially melts below $T_{\rm
S}$ on cooling. Our results provide compelling evidence that the ground state
of IrTe$_2$ is a commensurate 1/6 charge modulation, which originates from
periodic dimerization of Te atoms visualized by atomically resolved STM images.
