  LaTiO$_3$ is known as Mott-insulator which orders antiferromagnetically at
$T_{\rm N}=146$ K. We report on results of thermal expansion and temperature
dependent x-ray diffraction together with measurements of the heat capacity,
electrical transport measurements, and optical spectroscopy in untwinned single
crystals. At $T_{\rm N}$ significant structural changes appear, which are
volume conserving. Concomitant anomalies are also observed in the
dc-resistivity, in bulk modulus, and optical reflectivity spectra. We interpret
these experimental observations as evidence of orbital order.
