Nearly 1,900 years ago, Roman Emperor Hadrian built a great wall across Britain. It was 73 miles long, and divided the Roman province of Britannia from the realms of the “painted men” to the north. Why?

The northerners were not particularly dangerous. Even if they were, they could quite easily climb the wall—or row around it! Perhaps more importantly, Queen Boudicca’s rebellion proved that Britannia’s greatest threat was its native Celtic population. And what exactly was Hadrian protecting? Britain’s north was an empty expanse of pastures and forests. Who cares if tattooed peasants herded their sheep in the hills? Rather than wasting precious Denarii on a wall, Hadrian should have fortified Roman cities and spent the rest on bread and circuses!

Hadrian’s Wall has stood since its completion in 128 AD. It witnessed the fall of Rome, the Saxon invasions, and the Norman Conquest. It survived King John’s antics, Oliver Cromwell’s violence, and the Kaiser’s wrath. It outlasted Bath’s bathhouses, the Globe Theater, and it will certainly outlive the Shard and its ostentatious glass cousins at Canary Wharf. Men have lived and men have died. The wall remains.

This is why Hadrian built his wall. And this is why Trump must build his. A wall is not just brick and mortar, nor steel and concrete—it is an enduring symbol of a people’s commitment to their sovereignty, their brethren, and their future.

Romulus’ Legacy

Tradition has it that Romulus, the first king of Rome, drove his ox-plow around the city on April 21, 753 B.C. The resulting furrow demarcated the spiritual and legal boundary between Rome and “not Rome”—Rome existed only within this sacred boundary, the pomerium; everything beyond was simply territory. This meant that Roman law applied only to those citizens within the pomerium. Anyone beyond the boundary, be they citizen, slave, or foreigner, was subject to martial law. In this way, Roman sovereignty was linked to the land itself.

This was a radical departure from the Greek understanding of sovereignty. In ancient Greece, the main unit of political organization was the polis, which is often translated as city-state. The translation is misleading. A polis was not a city in the modern sense—it was not synonymous with a particular place or collection of buildings. For example, it was not uncommon for a polis simply to relocate in times of conflict—even Athens temporarily relocated to the Island of Aegina during the Persian Wars (499-449 B.C.). This is in stark contrast with Rome, which refused to evacuate in the face of the Carthaginian invasion under the famed Hannibal. Athens could move. Rome could not.

Likewise, a polis was not a state, as it existed independently of any particular government or code of laws. Consider how Greek poleis routinely changed from oligarchies to democracies and back again throughout the Peloponnesian Wars (431-404 BC)—but nevertheless retained a continuity of identity. The polis existed independent of its constitution. Compare this to Rome, which formally changed governmental systems twice in some 1,200 years (once, if you ask Octavian), and both regime changes were accompanied with an orgy of calumny followed by an ordeal of introspection and reinvention. Roman sovereignty was embodied in the law, and thus to replace the law was to replace Rome itself.

Greeks made laws, laws made Romans.

These two conceptions of sovereignty (and by implication, identity) help explain why Rome, rather than Athens, united the Western World.

To the Strongest . . .

The conquests of Alexander the Great (d. 323 B.C.) were a brilliant flash in the bleak march of history. Within just 13 years, Alexander had subjugated everything between the ancient Nile and the mysterious Indus. His was the greatest empire the world had ever seen. So electric was Alexander’s spirit and so impressive were his deeds, that he was deified in Egypt as the son of Amon Ra—of Zeus himself! He was a living Heracles. Yet Alexander’s empire crumbled like sand upon his death. Meanwhile, the empire’s successor states were fragile, held together only by spilt blood and sacrificed treasure. What went wrong?

Although Macedonian by birth, Alexander was raised Greek. His father, King Philip II, went to great pains to Hellenize his people by competing in the Olympic Games, avenging the Delphic oracle in the Third Sacred War, and hiring the famed polymath Aristotle to educate his son. As such, it is not surprising that Alexander’s conception of sovereignty was quintessentially Greek: what cohered his empire was not the rule of law, nor his disparate people’s loyalty to their homelands, but lineage. Consider Alexander’s two most famous attempts to consolidate his conquests.

First was Alexander’s apotheosis in Egypt. After occupying the Nile, Alexander crossed the Great Sand Sea to supplicate the Oracle of Amon Ra at the Siwa Oasis. There Alexander was deified, and so entered the Egyptian pantheon. No longer was he a conquering king—he was Egyptian god, like the pharaohs before him. Alexander made this detour because he assumed that sovereignty flowed through blood (in this case, divine blood), and thus the best way to secure Egypt was to become Egyptian by (re)birth.

Second were the Susa Weddings. Alexander’s attempt to consolidate his rule in Persia culminated in a mass marriage: he betrothed an Achaemenid princess and forced 10,000 of his men to take Persian wives, mostly against their will. Again, this highlights Alexander’s emphasis on common ancestry as being integral to sovereignty—Greeks could not become Persians, and Persians could not become Greeks, without comingling their blood. Lineage was the essence of Greek sovereignty.

Tying sovereignty to the people worked exceptionally well as long as the Greeks lived in relatively small, isolated, and homogenous communities—there is a reason King Leonidas’ 300 Spartans were able and willing to stand against Xerxes’ diverse myriads—but this paradigm failed in the Hellenistic kingdoms. Why?

The vast majority of Hellenistic subjects were not Greek and had no way of becoming Greek, so why should they care what happened to their Greek overlords? Why should they die for Antigonus the One-Eyed rather than Seleucus the Victor? After all, “they’re all Greek to me!” Most Hellenistic subjects lacked skin in the game, and this largely explains why Alexander’s empire fractured upon his death, why the successor states were constantly fragmenting, and why the Hellenistic world ultimately succumbed to Rome.

Caracalla’s Wisdom

We can sum up Rome’s expansion by paraphrasing Julius Caesar: they came, they saw, they conquered. What made Rome unique, however, was not its ability to conquer new lands, but its ability to assimilate new people, to turn barbarians into Romans.

The process of assimilation began early in Roman history with the formation of the Latin League, which granted Roman allies various privileges over the neighboring Etruscans. In doing so, Rome gave its allies a stake in its success—it put its skin in their game. This culminated with Rome granting varying degrees of citizenship to its allies following the Second Latin War (340-338 B.C.). Rome turned non-Romans into Romans.

The expansion of citizenship was Rome’s salvation: when King Pyrrhus of Epirus invaded Italy in 280 B.C. he could not overcome Rome’s manpower. At the time, half of Rome’s army consisted of allied peoples. There is little doubt that Pyrrhus would have been victorious had Rome stood alone. The same fate awaited the Carthaginian general Hannibal during the Second Punic War (218-201 B.C.). Although Hannibal killed or captured 30,000 Romans at the Battle of the Trebia River, 80,000 at the Battle of Cannae, and 20,000 at the Battle of Lake Trasimene, Rome eventually prevailed. Why?

Rome was not just the City of Rome. Rome was (most of) Italy, and Italy could sustain the losses. Rome continued to grow, granting citizenship to all peninsular Italians following the Social War (91-88 B.C.), and to people in Iberia and Gaul at Julius Caesar’s behest. Finally, Emperor Caracalla granted citizenship to all free men within the Roman Empire in 212 A.D. Rome owed its success to the fact that it was the first state in history to combine the scale of a Hellenistic Empire with the cohesion of a Greek polis. Rome was both Pericles’ Athens and the Empire of Alexander.

In short, Rome was the world’s first country—a land of laws inhabited by loyal citizens. It was not until Rome devolved into multifarious ethno-religious tribes that she finally fell.

Another Brick in the Wall

This brings me back to Hadrian, Trump, and walls.

As we have seen, Hadrian’s Wall was not built to keep people out like the Great Wall of China, nor was it built to keep people in like the Berlin Wall. And frankly, it protected little of economic value and nothing of strategic importance. This raises the question: why would Hadrian build his big, beautiful wall at the furthest-flung, least significant corner of the Roman Empire? Why not spend the resources bolstering the fortifications along the Rhine or the Danube? Why not wall the Anatolian passes to stymie the marauding Parthians?

The answer is that Hadrian’s Wall was not just a wall—it was an indelible symbol, a metaphor made manifest: it was Rome’s new pomerium, civilization’s sacred boundary wrought in stone. Behind the wall was Rome, a land of laws upheld by loyal citizens, beyond was hostile territory. Hadrian’s Wall needed to be built at the very edge of the Empire to show everyone—be they Roman or barbarian—that Rome was not just Rome. Rome was Britannia. Rome was Africa. Rome was Asia. And Rome would defend to the death every grain of sand and every blade of grass behind Hadrian’s Wall. Why? Because each was a part of Rome, and Rome was sacred.

America’s Founders envisioned our nation as a land of laws upheld by loyal citizens—America was a new Rome. And like Rome, one of America’s greatest strengths was in its exceptional ability to turn non-Americans into Americans, to create unity out of discord, and from this unity, strength. This is no longer happening, and this is why President Trump must build a wall.

In addition to keeping migrants out, America needs a wall to show everyone—be they American or foreign—that America is not merely a collection of competing individuals and tribes. It is not a whipping-boy for the military-industrial complex. It is not a plaything for globalists. And it is not a goody-bag for Third-World migrants to pillage at their pleasure. Instead, America is a land of laws inhabited by loyal citizens who will defend to the death every grain of sand and every blade of grass behind the wall. Why? Because each is a part of America, and America is sacred. Many Americans—and most of the world—forgot this.

We need to remind them. Build the wall.

Photo Credit: Herika Martinez/AFP/Getty Images