  An energy scan near the $\tau$ pair production threshold has been performed
using the BESIII detector. About $24$ pb$^{-1}$ of data, distributed over four
scan points, was collected. This analysis is based on $\tau$ pair decays to
$ee$, $e\mu$, $eh$, $\mu\mu$, $\mu h$, $hh$, $e\rho$, $\mu\rho$ and $\pi\rho$
final states, where $h$ denotes a charged $\pi$ or $K$. The mass of the $\tau$
lepton is measured from a maximum likelihood fit to the $\tau$ pair production
cross section data to be $m_{\tau} = (1776.91\pm0.12 ^{+0.10}_{-0.13}$)
MeV/$c^2$, which is currently the most precise value in a single measurement.
