Did the communication lag become a problem for the ever expanding Roman Empire?

I have to agree with @Felix Goldberg. Communication wasn't the real problem. Remaining in power most certainly was, for many emperors. The mortality rate of emperors was as high as gladiators. Not that many died peacefully in bed.

Communication was done with the cursus publicus which remained more or less in tact until the very end of the empire. That system had worked well when the empire was at its largest extend, so communication cannot be the real reason for its demise and split of the empire.

What I notice is that both provinces and military units progressively become smaller over time. Part of that may well be to make better management possible. A far more important reason is to make it more difficult to revolt.

A governor controlling a large part of Gaul with 4 or more legions is far more dangerous to the emperor than a governor that governs a much smaller province, especially if the military command is separate. The governor would hold political power but not military power to make a bid for the purple, and the military commander didn't have the political power to support him. In both cases the governor(s) and the general(s) had a lot less political and military power than in the past.

Which, at least for a short time, solved another problem: more governorships and military commands to share out to adherents. In other words: the pie was sliced in thinner slices to satisfy more people. The long term problem was that once more people shared in the pie, they invariably wanted a larger piece of it.

How was communication in the Roman Empire set up

The cursus publicus was the Roman equivalent of the Pony Express. All throughout the empire were stations where riders and important travelers could change horses and riders. That way a message could reach Rome within about 10-15 days.

The effect of increasing the size of Roman Empire affected the control of the Senate over the armies. While Rome was only a small city, the Senate was able to choose Consuls for each year, and rise an army for each campaign.
But, when Rome increased its size, it was necessary to keep armies far away of the city, so the members of the army started to be professional soldiers loyal to their commander, instead of citizens loyal to the city.
Civil wars in Rome started because soldiers were loyal to their Generals. And Generals were independent enough because they were far away of the city. Most rebellions in Rome started in remote places, not near Rome or Constantinople.

The first civil war, was because the Senate was afraid of Caesar, and asked him to leave his legions and return to Rome. He returned, but with his legions with him. Those legions were loyal to its General, because they fought together for almost ten years.

From Wikipedia

"In order to maintain control and improve administration, various schemes to divide the work of the Emperor by sharing it between individuals were tried between 293 and 324, from 337 to 350, from 364 to 392, and again between 395 and 480. Although the administrative subdivisions varied, they generally involved a division of labour between East and West. Each division was a form of power-sharing, (or even job-sharing) for the ultimate imperium was not divisible and therefore the empire remained legally one state—although the co-emperors often saw each other as rivals or enemies rather than partners."

That is probably the best evidence that the cost of communication rose to be impracticable; the Emperors divided the empire because it was not possible to exercise imperium.

I think it would be interesting to (a) examine the rise of the proconsul as an adaptation of the Roman Republican system to the increased cost of communication and (b) the general question of how the Roman Republic balanced delegation of power against the difficulty of maintaining oversight (I'm going to assert that within the context of your question the value of communications is the exercise of oversight) - but those questions are far beyond the scope of stack exchange. (

I think that the short answer to your question is: No. The Empire survived very well for about 400 years (let's say from the death of Augustus in 14 CE to circa 400 when the so-called migration of the peoples began to be felt in the Empire) with the same communications structure.

Ancient states required much less centralized decision making than modern ones and the cursus publicum system that was mentioned in another answer (there was a naval system as well, by the way), together with a considerable degree of autonomy given to governors, sufficed for the Empire's needs.

The division of the Empire had, in my opinion, more to do with political exigencies created by increasing external pressure, than with communications problems. There were more threats to respond to beginning with the Gothic invasions of the late 3rd century, but the Emperor could never trust a subordinate with too much military power, because the later was almost sure to turn upon him at some stage; the only practical solution that worked was to divide the Empire and its army. The problem here was not technological, it was political.

The Roman Empire had the cursus publicus, which maintained an infrastructure of horses and way stations. The messenger himself was supplied by the one sending the message. It was used for transporting messages, magistrates, and some heavy goods too. Important messages typically travelled at roughly 50 miles per day.