Abstract
Smooth Schubert varieties were rst characterized in terms of pattern avoidance by Lakshmibai and Sandhya. One way of classifying singularities in a variety is the Hilbert-Samuel multiplicity. We characterize the Schubert varieties of flag manifolds which have
Hilbert-Samuel multiplicity two or less at all points using the Rothe diagram. Our condition is relatively simple and visually easy to distinguish given the Rothe diagram of a Schubert variety. We also show that Schubert varieties with multiplicity two or less at all points
cannot be characterized by pattern avoidance.