  We have investigated the magnetic ground state of the antiferromagnetic
Kondo-lattice compounds CeMAl$_{4}$Si$_{2}$ (M = Rh, Ir) using neutron powder
diffraction. Although both of these compounds show two magnetic transitions
$T_{N1}$ and $T_{N2}$ in the bulk properties measurements, evidence for
magnetic long-range order was only found below the lower transition $T_{N2}$.
Analysis of the diffraction profiles reveals a commensurate antiferromagnetic
structure with a propagation vector $\mathbf{k}$= (0, 0, 1/2). The magnetic
moment in the ordered state of CeRhAl$_{4}$Si$_{2}$ and CeIrAl$_{4}$Si$_{2}$
were determined to be 1.14(2) and 1.41(3) $\mu_{B}$/Ce, respectively, and are
parallel to the crystallographic $c$-axis in agreement with magnetic
susceptibility measurements.
