In order to bring them into contact, you need to transport modern Somalia back in time to the early second century. The Somali economy is heavily dependent upon imports for food, energy, and technology, including military technology; a huge part of its economy is also comprised of remittances. Its government, such as it has a government, is propped up by international aid agencies. All imports, remittances, and aid cease immediately. Somalia's government collapses more or less overnight as Mogadishu descends into food riots. Over the next few months famine stalks through the land. Cannibalism is not uncommon. The state fragments almost immediately along clannish lines. Somalia becomes a patchwork of feuding warlords, fighting over rapidly diminishing supplies of food and fuel. Supplies of ammunition are seriously depleted over several months of vicious internecine warfare. Warlords along the frontier eventually figure out that they have somehow found themselves almost two thousand years in the past. They do the natural thing and begin conquering petty kingdoms for themselves, using their overwhelming advantage in firepower to subjugate tribesmen in what is now Kenya and Ethiopia. Word of these easy conquests reaches back to famished horde of refugees fleeing Mogadishu, which pushes out into East Africa in a disorganized mass of little warbands each looking to carve out their own little tribal domain. It takes about a year for trade routes to carry word of this miraculous catastrophe to Rome, several thousand kilometres distant. These are initially treated as fantastical rumours of a distant land, and largely ignored. After a few years, the persistence of these rumors leads to a diplomatic mission being despatched. By the time the Roman legate arrives in Mogadishu, several years have passed. Mogadishu's population is dramatically reduced, and most of the high technology has ceased to function due to the absence of spare parts and the scarcity of fuel. The city is no longer electrified. Ammunition stocks have long since been depleted. The local warlord has consolidated what fuel, ammunition, and functioning technology remain, and he conserves it jealously. The hundreds of minor warlords that pressed out into the African frontier have done the same in their respective territories. Modern technology has already reached the level of a magical artifact: decisively powerful, but rare and irreplaceable. The legate's primary objective is to return with some of these wonders, and he is authorized to make extravagant gifts in order to secure access to them. The real prize would be the technical volumes in Mogadishu University's library. Much of it would be well beyond the comprehension of Roman engineers, but it would probably not take them long to learn the rudiments of modern chemistry and metallurgy, the principles of steam power, and the use of coal (available in abundance in modern Britain, a fact which would also be apparent from library's geological texts). The Romans would find the concept of a railroad particularly fascinating. Long before Somalis could come into military contact with Rome, technological diffusion would have set off an industrial revolution in the Roman Empire. The Rome the Somalis encounter along frontier of their warlord expansion would have legions equipped with muskets, triremes with cannons, and steam trains thundering across its new railway system. Meanwhile the Somalis themselves, perfectly incapable of even manufacturing new 7.62 for their AKs, much less repairing their technicals and helicopters, would be back to riding on horseback and fighting with spears, arrows, and black-powder muskets. What high technology they still have would be held in reserve as strategic weapons to be used only in dire emergencies. When war finally arrives the Somali technological advantage has been almost entirely eroded. The conflict is decisive. Rome crushes them.