  We study the D-brane solutions to type IIB superstring in ten dimensions and
find interpretation in terms of compactification of a twelve dimensional
three-brane of (a specific) F-theory on a torus $T^2$. In this frame-work,
there also exist a two-brane which may be argued to be equivalent to the
three-brane by utilizing the electric-magnetic duality in eleven dimensions. In
this context, we propose for the existence of an isometry in one of the
transverse directions to the three-brane in F-theory. As a consequence the
two-brane may be identified with the three-brane in twelve dimensions itself.
The twelve dimensional picture of D-branes in type IIB theory suggests for the
reformulation of type IIB superstring in terms of three-brane of F-theory.
