Phase 1
1347: Entry shock through contested ports
Initial transmission is a logistics event. Two strong maritime routes connect Caffa to Constantinople and Messina. The system still looks sparse, but both endpoints are high-turnover nodes.
The Caffa vector
The traditional narrative begins with a siege. Mongol forces besieging the Genoese trading post at Caffa on the Black Sea coast reportedly catapulted plague-infected corpses over the walls — an early instance of biological warfare. Whether this caused the outbreak or whether the rats and fleas had already crossed the siege lines is debated. What matters for the network model is the result: Genoese ships fled Caffa carrying infected crew and cargo westward along established trade corridors.
Why these ports
Constantinople and Messina were not random endpoints. They were the two highest-throughput nodes in the eastern Mediterranean trade system. Constantinople handled traffic from the Black Sea, the Aegean, and the overland Silk Road terminus. Messina sat at the bottleneck between the eastern and western Mediterranean basins. An epidemic that reached both simultaneously had access to every major trade route in the known world.
- Early spread remains mostly maritime.
- Risk profile is concentrated in fewer cities.
- Route redundancy is low, so each successful arrival matters more.
"The Mongols catapulted their own dead over our walls. We sailed before we understood what we carried."
Caffa — Genoese garrison clerk
"The ships from Caffa arrived on schedule. Grain manifests looked normal. The sailors did not."
Constantinople — Harbor customs officer
"Twelve galleys. Black swellings big as eggs on the crew. Stink like nothing I smelled before. We should have cut the ropes and pushed them back out. Nobody gave the order. Nobody."
Messina — Dockworker
Phase 2
1348: Mediterranean saturation
The second season adds lateral corridors. Messina, Genoa, Venice, Marseille, and Barcelona become a relay ring. Once this ring appears, interruption requires coordinated controls, not single-port action.
The relay ring
By spring 1348, the plague is no longer traveling from one origin point. It is circulating in a loop. Messina infects Genoa, Genoa infects Marseille, Marseille infects Barcelona, Barcelona trades back to Genoa. The distinction matters: a linear chain can be broken at any point. A ring cannot — cutting one link just means the disease arrives via the other direction, slightly delayed.
Trade that could not stop
Medieval Mediterranean commerce did not have a pause button. Ships sailed on seasonal schedules driven by wind patterns. Contracts for wool, silk, spices, and grain were binding. A merchant who refused to ship lost his investment and his reputation. The same economic logic that made these cities wealthy made them vulnerable: they could not afford to stop trading, and they did not stop until it was too late.
- Maritime routes outnumber inland routes.
- Multiple equivalent paths now exist.
- Regional exposure stops being local.
"We chased the Messina ships out with flaming arrows. It did not matter. The rats were already ashore."
Genoa — Merchant shipowner
"We ordered forty days of isolation for incoming vessels. Quaranta giorni. It was too late for the first wave, but the word would outlast us all."
Venice — Council health inspector
"One ship. That is all it took. They said it came from the east. My wife was dead within the month. My eldest son before her. The baby after. I sat in the house with them for two days because there was no one left to help me carry them out. The street was emptier than Lent. I say that because I cannot say what it really was. There is no word for a street where everyone you knew is gone and the doors stand open and the dogs eat what they find. I am a fisherman. I mend nets. I cannot mend this."
Marseille — Provençal fisherman
"Trade did not stop. That is the thing no one says. The wool still came. The silk still came. The dye vats still needed tending. And with the bales, the dying. I stained my hands red every morning and buried my neighbors every evening."
Barcelona — Cloth dyer
Phase 3
Late 1348: Inland relay compounds the wave
Once inland corridors engage, the coast is no longer the only lever. Paris and London become bridge nodes. Even if sea arrivals weaken, connected interior networks can keep pressure elevated.
From harbor to hinterland
The plague moved inland along the same routes that moved everything else: river barges, pack trains, pilgrim roads, military supply lines. The shift from maritime to overland transmission changed the epidemic's character. Sea routes were fast but narrow — a quarantined port could block them. Inland routes were slower but diffuse, branching into market towns and villages with no inspection apparatus at all.
The Paris Faculty report
In October 1348, the medical faculty of the University of Paris issued a formal report attributing the plague to a conjunction of Saturn, Jupiter, and Mars that corrupted the air. It was the most authoritative medical analysis available. It was also useless. The report circulated widely — Benedictow traces its influence across Latin Europe — and gave civic authorities a framework for response that had nothing to do with contagion. They organized processions and bonfires to purify the air while rats moved freely through the granaries.
- Transmission shifts from harbor to hinterland.
- Risk index remains high with mixed link types.
- Delay policies need both port and city enforcement.
"We were the first to mandate trentino — thirty days outside the walls before entry. Others would copy us. Eventually."
Ragusa — City elder
"The faculty declared it was a corruption of the air from a conjunction of Saturn, Jupiter, and Mars. We wrote it in Latin and sealed it with the university stamp. Three of the faculty who signed it were dead before the ink dried. I am the fourth signatory. I write this with the windows shut."
Paris — University physician
"Came up the road from the ports. Bristol first, then along the trade roads. By autumn the graveyards were full. They dug new pits east of the wall. Big ones."
London — Wool merchant
"The king ordered processions through the streets to beg mercy from Almighty God. Hundreds walked shoulder to shoulder, singing, weeping, sharing breath. The processions spread it faster. We wrote the death tallies. We learned nothing in time."
Valencia — Municipal scribe
Phase 4
1349 to 1350: Northern exhaustion, not collapse
The network keeps moving north through shorter links. Route intensity softens, but diffusion continues where labor, grain, and military movement preserve contact frequency.
The labor crisis begins
By 1349, the epidemic's economic consequences are already visible. Fields go unharvested because the laborers are dead. Workshops close because the craftsmen are dead. The supply chains that carried the plague now carry shortages. Wool production in England drops sharply; Flemish weavers run out of raw material before the plague even reaches Bruges. The disease moves along trade routes, and so does the economic damage — sometimes arriving before the disease itself.
River corridors
Northern European spread followed rivers more than roads. The Danube, the Rhine, the Seine, the Thames — each one functioned as a high-speed inland route that connected port cities to interior markets. Bargemen and their cargo moved continuously along these corridors, and the plague traveled with them. Unlike roads, which could be blocked by a locked gate, rivers could not be quarantined without shutting down entire regional economies.
- Inland and short sea links dominate.
- Node count plateaus while local mortality remains severe.
- Regional systems begin fragmenting at different speeds.
"The English wool stopped coming. No wool, no thread. No thread, no cloth. No cloth, no wages. Then the weavers started dying anyway. The looms went quiet one by one, like candles blown out down a corridor."
Bruges — Flemish weaver
"The northern routes held longer. We thought distance might save us. It only delayed what was already certain."
Hamburg — Hanseatic trader
"It crept inland along the river. The Danube, which God gave us for commerce and sustenance, carried the pestilence on the backs of bargemen who did not know they were already dying. I administered last rites until my voice gave out. Then I administered them in silence."
Vienna — Augustinian friar
"The Nile ships kept running. Cairo needed grain. Alexandria needed to believe the season would end. It did not end."
Alexandria — Grain warehouse keeper
Phase 5
1351 to 1352: Controls and distance blunt the wave
By the final phase, route pressure is lower and patchier. Delays, inspections, and exhausted susceptible populations combine into slower spread. The mechanism weakens before memory does.
What quarantine actually did
The cities that fared best were the ones that imposed trade restrictions early and enforced them consistently. Ragusa's thirty-day isolation policy — the trentino — predated the Venetian forty-day quarantina and may have been the first formal quarantine in European history. Milan's Visconti rulers sealed infected houses with the occupants inside, healthy or not. The measures were brutal, inconsistent, and unevenly applied. But they worked where they were enforced, because they interrupted the contact chains that the network model depends on.
The survivors' world
By 1352, between a third and a half of Europe's population was dead. The demographic shock reshaped everything that followed: labor became scarce and expensive, serfdom weakened, wages rose, land values fell. The surviving workers had leverage they had never possessed before. The Black Death did not end medieval Europe — but it broke the economic logic that medieval Europe ran on.
- Long maritime links are easiest to suppress.
- Short inland links linger as residual risk.
- Policy works better when implemented before ring saturation.
"Civilization shrank with the decrease of mankind. Cities and buildings were bared. Roads and signposts were obliterated."
Tunis — Ibn Khaldun, historian
"We sealed the houses. Three planks across the door, the sign of the cross in red paint. I heard them inside, the well and the sick together. The Visconti ordered it. I carried it out. God will judge which of us was right."
Milan — Municipal guardsman
"When it passed, the land was cheap and the living were few. A ploughman could name his wage. A maid could choose her master. That had never happened before, not in my father's time nor his father's. The dead bought that with their dying, though they did not mean to."
East Anglia — Manorial steward