The Euclidean black hole has topology ${\mathit{gerR}}^2$×${\mathit{scrS}}^{\mathit{d}\mathrm{-}2}$. It is shown that, in Einstein’s theory the deficit angle of a cusp at any point in ${\mathit{gerR}}^2$ and the area of the ${\mathit{scrS}}^{\mathit{d}\mathrm{-}2}$ are canonical conjugates. The black hole entropy emerges as the Euler class of a small disk centered at the horizon multiplied by the area of the ${\mathit{scrS}}^{\mathit{d}\mathrm{-}2}$ there. These results are obtained through dimensional continuation of the Gauss-Bonnet theorem. The extension to the most general action yielding second order field equations for the metric in any spacetime dimension is given.

• Received 27 September 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.957