  We present a simple mechanism for obtaining large-field inflation, and hence
a gravitational wave signature, from string theory compactified on twisted
tori. For Nil manifolds, we obtain a leading inflationary potential
proportional to phi^(2/3) in terms of the canonically normalized field phi,
yielding predictions for the tilt of the power spectrum and the
tensor-to-scalar ratio, $n_s\approx 0.98$ and $r\approx 0.04$ with 60
e-foldings of inflation; we note also the possibility of a variant with a
candidate inflaton potential proportional to phi^(2/5). The basic mechanism
involved in extending the field range -- monodromy in D-branes as they move in
circles on the manifold -- arises in a more general class of compactifications,
though our methods for controlling the corrections to the slow-roll parameters
require additional symmetries.
