Einstein insisted throughout his life that the signal achievement of his general theory of relativity was its general covariance. How are we to reconcile this with the now common view that general covariance merely expresses a definition, our freedom to label events with any set of numbers we like? There is, I believe, a natural reading for Einstein's claims that does make perfect sense. It requires us to adopt a physical interpretation of relativity theory that is now no longer popular, so the natural reading will no longer have intrinsic interest. It will, however, allow us to make sense of Einstein's claims and his program.