  We use powder x-ray diffraction to study the effect of pressure on the
crystal structure of the honeycomb rhodate Li$_2$RhO$_3$. We observe
low-pressure ($P$$<$$P_{c1}$ = 6.5 GPa) and high-pressure ($P$$>$$P_{c2}$ = 14
GPa) regions corresponding to the monoclinic $C2/m$ symmetry, while a phase
mixture is observed at intermediate pressures. At $P$$>$$P_{c2}$, the honeycomb
structure becomes distorted and features short Rh--Rh bonds forming zigzag
chains stretched along the crystallographic $a$ direction. This is in contrast
to dimerized patterns observed in triclinic high-pressure polymorphs of
$\alpha$-Li$_2$IrO$_3$ and $\alpha$-RuCl$_3$. Density-functional theory
calculations at various pressure conditions reveal that the observed rhodium
zigzag-chain pattern is not expected under hydrostatic pressure but can be
reproduced by assuming anisotropic pressure conditions.

Strongly Correlated Electrons