The roots fuse, which creates a pretty cool effect.
It sounds like a menace, doesn't it? It can be, but the tree is so attractive that in Australia, less desirable trees are "replaced" with strangler fig trees, which are perfect for shade or climbing!
I ♥ Strangler Figs
(For more information and neat pictures, try http://waynesword.palomar.edu/ploct99.htm)