When most people think about ancient Rome, it is likely they are picturing huge stone amphitheaters, gladiators, and roving armies. However, it is the massive and almost immeasurable unseen logistical efforts of the Empire that demonstrate the true genius of Rome. Much has been written about Rome’s legions and the wars they fought across a territory that covered more than 1.5 million square miles—from modern-day Britain in the west to Iraq in the east. Yet these military operations would not have been possible without naval logistics on a grand scale, since the movement of men and matériel by sea was often swifter and more efficient as compared to land routes.

In the year 43 AD, Rome invaded Britain, a feat that required a staggering movement of troops, horses, grain, and equipment. The difficulties and complexities associated with amphibious warfare are immense. Today it would require extensive use of computers, electronic communications, tide charts, weather predictions, and thousands of other variables, but the Romans had no such capacity. What they did have was an exceptional level of organization—which made for a relentless method of warfare.

Historians note various reasons for the Roman invasion of Britain, including Emperor Claudius’s need for prestige, new avenues for taxation, access to natural resources, and regional politics. But the baseline is that the early Roman Empire was focused on expansionism. Assimilating peoples and nations brought resources, slaves, land, and taxes into the coffers. With these attainments in mind, four Roman legions totaling approximately 20,000 troops were dispatched to Britain’s shores in nearly 1,000 ships.

Many sources put the entire force—including servants, slaves and auxiliary combat detachments—at between 35,000 and 40,000. Before the invasion these troops were moved up from Central and Southern Europe, a sizable task. Researchers estimate that the average Roman soldier had 54 to 100 pounds of equipment, which would have created a significant baggage train of wagons and mules—all needing transport by ship.

In addition, the army, and the individual soldiers, routinely had slaves and servants who traveled with them during combat operations. Estimates range between 400 and 1,400 per legion, thus four legions would have brought along 1,600 to 5,600 additional persons needing to be transported.

The movement of troops and personnel was enormous, but the amount of shipping needed was even greater, as a large number of horses, mules, and other animals would have accompanied them to carry equipment and serve the cavalry. It is estimated that the average legion required 1,400 mules, which would mean at least 5,600 needed for the invasion. Some researchers put that number at upwards of 10,000. Since the Romans made use of heavy siege tools and battlefield artillery (carroballistae, onagers/catapults, towers, and rams), this number is not outside the realm of possibility. Artillery likely comprised a large portion of a typical military baggage train. There are historical references indicating a Roman legion might have 60 to 65 pieces of artillery. Each legion thus would require 70 wagons and 160 animals for these weapons and their ammunition, equating to 280 wagons and 640 animals. A mule weighs between 800 and 1,000 pounds, thus adding a substantial increase in the aggregate need for shipping.

In addition, each legion usually had a detachment of approximately 150 to 400 cavalry (equites legionis) who were often used for reconnaissance and screening. It would seem that initially 600 to 1,600 horses would be needed, but spares also would have been required because of attrition stemming from accidents, combat, and disease. Adding to this, senior officers likely had more than one horse.

The transport of horses by ship is a delicate process that requires special attention to loading and unloading, especially for an amphibious landing. Ancient sources observed the negative impact of moving animals by sea. There is also the possibility that elephants were part of the invasion force. A substantial amount of food/fodder for animals would have been shipped, because the Romans would not have known what kind of reception they would receive upon landing on the shores of Britain; free-grazing might not be possible. When Julius Caesar had made a brief invasion of the island nearly a century before, his forces met with immediate armed resistance on the beach, and they soon returned to the continent. It was one of the first recorded mentions in history of ship-to-shore fire.

All armies march on their stomachs, and Rome’s was no exception. In a time when the average citizen had a rather limited diet, soldiers are known to have had quite a bit of variety. Their ration consisted mainly of grain (the frumentum) for bread and other foodstuffs (the cibaria). Research has shown that cattle, pigs, cheese, beans, oil, and wine, along with numerous fruits and vegetables, were frequently consumed in garrisons.

It cannot be presumed that troops on the move in combat would eat like those stationed in garrisons, but also it is unlikely that grain/bread could sustain tens of thousands of men burning through large sums of daily calories for long periods of time. Herds of animals likely were brought along to provide meat, again increasing the need for transport. It has been calculated that a six-month supply of grain for 40,000 personnel would have weighed 6,967 tons (nearly 14 million pounds). A few decades prior to the invasion of Britain, when the Roman Army was fighting in Germany, the soldiers likely were consuming 25 tons of wheat and 7.5 tons of other foods, as well as nearly 25 tons of barley for their animals—each day. The cross-sea provision of food for the soldiers in Britain must have been a monumental naval task in and of itself.

It is not known exactly when in 43 AD the invasion took place, but sources point to late spring or early summer. The southeastern coast of Britain is not known for its fine weather and hospitable currents even during the warmer months. Caesar’s earlier invasion was greatly delayed due to gales. Sea temperatures in May are in the low 50s. Air temperatures are in the upper 50s to low 60s, with nights in the mid- to upper 40s, which is important to note, since Caesar’s brief prior invasion force likely had arrived at night. This allowed for a full day’s worth of daylight for the landing and disembarkation. However, this also meant that the soldiers and animals were in open-air ships for several hours during the crossing and prior to landing. It is likely that the arrival of the invasion force in 43 AD also occurred at night. This would have required an enormous amount of planning, coordination, and signaling of various forms to keep the fleet operating in unison.

Sources note that the invasion likely required 724 to 1,041 ships. Even if it took multiple trips (and thus fewer vessels) to get all of the troops and equipment across, it was still a sizable fleet. Estimates are that a single ship could hold 80 to 120 personnel or 30 horses. The number of trees needing to be felled, and the lead time to build these vessels, is staggering. Reconstruction archaeology of a small Roman riverine patrol boat, which would have held 20 to 22 people and weighed six tons, required 18 trees. The average weight of a Roman cargo vessel was between 33 and 44 tons. Thus, building nearly 1,000 would have consumed tens of thousands of trees. Needless to say, the creation of such a fleet was an industrial undertaking with regard to felling, prepping, and moving of timber.

It is known that the Romans would transport timber across great distances when necessary, and the legions may well have participated in this process. That makes sense, since it literally would require a well-organized army to accomplish such an enormous task. There are many historical references to the use of the army for building bridges, aqueducts, fortifications, and roads. For example, the 72-mile-long fortification line known as Hadrian’s Wall was built in Britain by the legions in the early part of the 2nd century.

Greco-Roman shipbuilders were keenly aware of the specific properties and hardiness of different types of wood. Analysis of three Roman cargo vessels found in the harbor of Naples, Italy, noted that many different types of trees were used in each one depending on their various properties of sturdiness, straightness, and resistance to decay in water.

As for other needs, several years before invading Britain the previous emperor, Gaius (known as Caligula), had contemplated the endeavor and ordered the initial preparations for the attack, including the building of ships. He also built portions of the naval port at Gesoriacum (modern day Bolougne) and its lighthouse—all of which likely played a role in 43 AD.

The Roman invasion of Britain required a massive logistical effort that must have taken years to prepare. Each individual supply requirement (food, ships, lumber, horses, etc.) was an astronomical task in and of itself. Roman naval forces were able not only to provide for a successful amphibious assault, but also to sustain it for months and years to come. Over time, this would become the nucleus for the Classis Britannica, one of the few Roman fleets outside of the Mediterranean. For the next three and a half centuries, Britain would be colonized and ruled by Rome as a vassal nation.