We present an assessment of the (6s2) S01 → (6s6p)P03 clock transition frequency in Hg199 with an uncertainty reduction of nearly 3 orders of magnitude and demonstrate an atomic quality factor Q of ∼1014. The Hg199 atoms are confined in a vertical lattice trap with light at the newly determined magic wavelength of 362.5697±0.0011nm and at a lattice depth of 20E R. The atoms are loaded from a single-stage magneto-optical trap with cooling light at 253.7nm. The high Q factor is obtained with an 80ms Rabi pulse at 265.6nm. We find the frequency of the clock transition to be 1128575290808162.0±6.4(syst)±0.3(stat)Hz (i.e., with fractional uncertainty=5.7×10 -15). Neither an atom number nor second order Zeeman dependence has yet been detected. Only three laser wavelengths are used for the cooling, lattice trapping, probing, and detection.