Duality of type II 7-branes and 8-branes

We present a version of ten-dimensional IIA supergravity containing a 9-form potential for which the field equations are equivalent to those of the standard, massless, IIA theory for vanishing 10-form field strength, F_{10}, and to those of the `massive' IIA theory for non-vanishing F_{10}. We present a multi 8-brane solution of these equations that generalizes the 8-brane of Polchinski and Witten. We show that this solution is T-dual to a new multi 7-brane solution of S^1 compactified IIB supergravity, and that the latter is T-dual to the IIA 6-brane. This result is made possible by the construction of a new {\it massive} N=2 D=9 supergravity theory. We also discuss the 11-dimensional interpretation of these type II p-branes