We report on the Lamb-Dicke spectroscopy of the doubly forbidden (6s<SUP>2</SUP>)S01<-->(6s6p)P03 transition in Hg199 atoms confined to a vertical 1D optical lattice. With lattice trapping of &#8818;10<SUP>3</SUP> atoms and a 265.6 nm probe laser linked to the LNE-SYRTE primary frequency reference we have determined the center frequency of the transition for a range of lattice wavelengths and at two lattice trap depths. We find the Stark-free (magic) wavelength to be 362.53(0.21) nm---essential knowledge for future use of this line in a clock with anticipated 10<SUP>-18</SUP> range accuracy. We also present evidence of the laser excitation of a Wannier-Stark ladder of states in a lattice of well depth 10E<SUB>R</SUB>.