  We report Coulomb drag measurements between vertically-integrated quantum
wires separated by a barrier only 15 nm wide. The temperature dependence of the
drag resistance is measured in the true one-dimensional (1D) regime where both
wires have less than one 1D subband occupied. As a function of temperature, an
upturn in the drag resistance is observed in three distinct devices at a
temperature $T^* \sim 1.6$ K. This crossover in Coulomb drag behaviour is
consistent with Tomonaga-Luttinger liquid models for the 1D-1D drag between
quantum wires.
