Horus is a communication architecture that treats a protocol as an abstract data type. Protocol layers can be stacked on top of each other in a variety of ways, at run-time. This paper starts out with describing the many classes of protocols that can be supported this way. Next, we describe the Horus object model that we designed for this technology, and the interface between the layers that makes it all work. We then present an example layer which implements a group membership protocol. Then, we look at a example stack of protocols, which provides fault-tolerant, totally ordered communication between a group of processes. We conclude with presenting some remaining challenges in our project.