  We report observation of the $\rm 5S_{1/2} \rightarrow 5D_{5/2}$ two-photon
transition in Rb vapor at 778 nm, using an external cavity diode laser system
and a heated vapor cell. The spectra in the two isotopes show well-resolved
hyperfine transitions. The peaks are Doppler free, and have a Lorentzian
lineshape with a typical linewidth of 2.2 MHz. This linewidth is larger than
the natural linewidth of 300 kHz, but is still 5--10 times smaller than the
linewidth for single-photon transitions in the D$_2$ line. Since the absolute
frequency of this transition is measured with 8 kHz precision, it can form a
better secondary reference in the optical regime compared to the D$_2$ line.
