  We have measured the geopotential difference between two locations separated
by 457 km by comparison of two optical lattice clocks via an interferometric
fiber link, utilizing the gravitational redshift of the clock transition
frequency. The $^{87}$Sr clocks have been compared side-by-side before and
after one of the clocks was moved to the remote location. The chronometrically
measured geopotential difference of $3918.1(2.4)\,\mathrm{m^2 \, s^{-2}}$
agrees with an independent geodetic determination of
$3915.88(0.30)\,\mathrm{m^2 \, s^{-2}}$. The uncertainty of the chronometric
geopotential difference is equivalent to an uncertainty of $24~\mathrm{cm}$ in
height.
