  We introduce the notion of the ell-weight lattice and the ell-root lattice
adapted to the study of finite-dimensional representations of quantum affine
algebras. We then study the ell-weights of the fundamental representations and
show that they are invariant under the action of the associated braid group, in
the case when the underlying simple Lie algebra is of classical type. As an
application of this result we are able to give explicit formulas for their
q-characters. An example is worked out in detail in Section 5. Finally, we
describe the blocks in the category and prove that they are parametrized by the
quotient of the ell-weight lattice by the ell-root lattice.
