Sermons on the Gospel Readings
Up until the modern era, with the advent of two-way radios, when generals needed to communicate with their commanders in the field, the most reliable method was to dispatch a runner. This was true in peacetime as well as wartime. Kings who wanted to communicate with important people in their far-flung empires made use of runners. It worked in reverse as well. Those in the field, those who were overseeing some project at a distance from their king or general, would reply by sending runners back with messages in response.