The mechanisms for the development of accretionary prisms in subduction complexes is numerically simulated using finite element plasticity analysis and the Barbados problem as an example. The accreted and subducting sediments are modeled as elastoplastic continua separated by rigid-plastic contact elements to simulate the thrusting mechanism. Results of the analyses demonstrate the importance of both lateral compression and topographic slope in the development and propagation of accretionary prisms in the Barbados subduction complex, affirming the analytical theory on the mechanics of thin-skinned fold-and-thrust belts presented by Chapple <1978>. Numerical analyses also reveal that the shape of the accretionary prism requires a critical balance in material characteristics such as the frictional strength of the basal layer, the modulus of the d¿collement, and the flow laws governing the yielding of the elastoplastic accretionary prism itself. Finally, it is shown that, unless the high normal stress at the base of the overriding plate is counteracted by a high fluid pressure localized in the d¿collement region, the frictional component of the basal traction will make the horizontal propagation prisms difficult. ¿ American Geophysical Union 1989