We present a rotational Raman spectrum for benzene with single-MHz resolution, more than a 100-fold improvement on literature data and sufficient to partially resolve K-splitting in some bands. Spectra for a frequency range of 0 to 500 GHz were measured through the observation of a coherent rotational wave packet in the time domain over a time scale of 1 microsecond. Spectroscopic frequencies were referenced to a GPS-stabilized clock. Fitted molecular constants of B = 5689.2671(±52) MHz, DJ = 1178(±50) Hz, and DJK = -2300(±120) Hz agree with results from some high-resolution rovibrational and rovibronic spectra but contradict others.