Note the small cube shaped structures at the top of each pier; these fit into the base of the bridges and also can be glued for further strength. Although this image shows the piers rising from a flat surface they can also be used to support bridges over valleys which drop down from track level.
The Märklin and Faller bridge systems are not compatible, but, with modification (i.e., cutting and fitting), they may be used with each other.
If you are using the overhead catenary, the Märklin 8913 mast snaps directly on the Märklin bridges. Faller makes a plastic piece which is glued to the bridge; then the 8911 mast is modified by cutting the base of the mast before being attached to the Faller bridge mount.