  A measurement of the cosmic-ray spectrum for energies exceeding
$4{\times}10^{18}$ eV is presented, which is based on the analysis of showers
with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger
Observatory between 1 January 2004 and 31 December 2013. The measured spectrum
confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$
eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with
index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by
a smooth suppression region. For the energy ($E_\text{s}$) at which the
spectral flux has fallen to one-half of its extrapolated value in the absence
of suppression, we find
$E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$
eV.
