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 $E_text{s}=(5.12pm0.25,text{(stat)}^{+1.0}_{-1.2},text{(sys)}){times}10^{19}$ eV.
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