Candelas and Font introduced the notion of a 'top' as half of a three
dimensional reflexive polytope and noticed that Dynkin diagrams of enhanced
gauge groups in string theory can be read off from them.
We classify all tops satisfying a generalized definition as a lattice polytope
with one facet containing the origin and the other facets at distance one
from the origin.
These objects torically encode the local geometry of a
degeneration of an elliptic fibration.
We give a prescription for assigning an affine, possibly twisted Kac-Moody
algebra to any such top (and more generally to any elliptic fibration
structure) in a precise way that involves the lengths of simple roots
and the coefficients of null roots.
Tops related to twisted Kac-Moody algebras can be used to construct string
compactifications with reduced rank of the gauge group.