In the semi-democratic Empire known as the Aurean Dominate, the small peninsula of Sparteia has seen a population explosion over the past two centuries or so. Located in Argentolia, the most populous (and 2nd largest by land area, around the size of the continental US) province of the Aurean Dominate, the Sparteia peninsula (around the size of Greece) was, for most of its history, little more than a stopover point for ships making voyages between the Capitol to the southwest and the gold-rich mountains of Monsaltu to the east. Now, 4 of the 10 largest cities in Argentolia are in Sparteia. What would be a good reason for a mass migration to such a region like this to occur?

Some background on Sparteia:

The peninsula is topographically extremely flat and marshy in the north, to the point where around 31% of the peninsula is considered wetlands. However, the Sparteian Alps begin to rise in the center and start running down the peninsula, making the south's terrain much more rugged. Generally, the east coast of Sparteia has a tropical rainforest climate while the west coast has a drier tropical savanna climate due to the Sparteian Alps' rain shadow. The north has a tropical monsoon climate transitional between the two. Some of the higher elevations in the Sparteian Alps experience a temperate Mediterranean climate. Like the rest of Argentolia's tropical north, Sparteia experiences the Pontic Monsoon in the slighyly cooler months from April-August, in which torrential downpours from the Pontic Ocean to the north contribute the vast majority of the area's annual rainfall. For example, Nirossos Bay on the east coast of Sparteia receives an average of 395 mm of rainfall in the month of June alone, while receiving only 72.6 mm in the warmest month of January.

While these monsoons are very useful for agriculture in other parts of Argentolia's north, Sparteia is almost entirely composed of limestone and has thin, chalky soils that have greatly limited agriculture in the region. Additionally, much of what Sparteia has historically grown are cash crops like coffee, rubber, sugarcane, coconuts, and oil palms on large plantations owned by wealthy Aureans who often do not even live in Sparteia. Food crops, mostly consisting of rice, citrus, mangoes, and bananas, are generally grown on a small scale by village-level subsistence farmers. The small portions of the more temperate Sparteian Alps that can be used for agriculture are almost completely used up by similar wealthy plantation owners as in the north, with wine and olive oil plantations dominating the valleys between the peaks.

The rugged and mountainous south of Sparteia is also known for Sparteian Rangers, a culture of semi-nomadic zebra riders dating back to before the Aurean Dominate conquered the region. Most of them are content to peacefully herd protoceratops and psittacosaurus or serve as light cavalry in the Aurean Military, but enough of them turn to banditry and become highwaymen to make traversing the Sparteian Alps somewhat dangerous.

Due to being almost completely surrounded by coral reefs, Sparteia had a sizable seafood industry even prior to the population boom. Ammonite, spiny lobster, goliath grouper, xiphactinus, and giant reef octopus (giant Pacific octopus but tropical) are all local delicacies.

Prior to this population boom, Zanclatis in the north was the only one of Sparteia's cities to host more than 100,000 residents. Now, 7 of Sparteia's cities (Zanclatis, Sozippa, Nirossos Bay, Cape Diosidos, Rizyra, Pheraci Beach, and Porta Burdigala) pass this benchmark, with 4 of them (Zanclatis, Sozippa, Nirossos Bay, and Cape Diosidos) in Argentolia's top 10 largest cities and 3 of them (Zanclatis, Sozippa, and Nirossos Bay) reaching a population of 1 million or more.

The technology level of the Aurean Dominate would most closely resemble that of the early to mid Ottoman Empire, although the dominant culture is much more Greco-Roman inspired but also varies somewhat by region. Sparteia specifically has some additional al-Andalus and Caribbean flair to it in some aspects, with much of the urban architecture being very Mudejar-looking and the cuisine using tropical ingredients like plantains and coconut milk. Little has changed in the Aurean Dominate technologically since before the population boom, thanks in part to the Aurean Senate's insistence on strict isolationist policies.

enter image description here Koppen climate map of Sparteia (cities w/ >10k residents in black, >100k residents in white, 10 largest cities in Argentolia province in green). The peninsula where Rigona is is part of the Capitoline Peninsulas rather than Sparteia, so ignore it. Rizyra and Lindesos are generally considered part of Sparteia and have experienced similar population growth, although they are outside the core peninsula.

enter image description here Koppen climate map of Argentolia as a whole (same color coding applies to cities as described above, with the addition of purple areas being neighboring provinces)

  • 1
    $\begingroup$ A big increase in food input would directly cause a big increase of population, for most lifeforms.. $\endgroup$
    – Manuki
    Jul 10, 2023 at 13:21
  • $\begingroup$ The maiden voyage of the SS Giganticus(or fleet of ships), holding 10x more cargo and being 2x as fast, starts a boom as 10x more people are need to manage the new levels of cargo and support staff. The roads have to be widened and maintained as well as the rest of the cities infrastructure. Giant warehouse on normally worthless land. $\endgroup$
    – cybernard
    Jul 11, 2023 at 14:30
  • $\begingroup$ I don't have a full answer, but to add natural growth answers to these 'influx' answers, I'd say that 1) if they were used to fighting and breeding, and the fighting stops, then the population booms. This could be a disease or other reason for dying going away, instead of fighting. 2) If a population has a reason to change their mindset about children, that can affect pop. quickly. After an attempted genocide, the almost-victims typically have as many kids as they can, East Timor is a current example. A religion change could affect this as well. $\endgroup$
    – MacIsaac
    Jul 11, 2023 at 17:43
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    $\begingroup$ Suddenly becoming remarkable. For example, a gold rush. $\endgroup$
    – user458
    Jul 11, 2023 at 20:24

9 Answers 9


Marginal Lands Made Productive (for Food)

(For a historical example...) Ireland was a place with relatively little good farmland and most land better suited for grazing. This created a bit of a calorie-bottleneck because there was only so much room for crops while grazing animals require a lot of time and land relative to the amount of food they produce. The introduction of the potato - which was calorie-dense and could be grown on some of the poorer soils - helped farmers much more easily cover their personal caloric needs and allowed a greater share of their better crops and meat/dairy to be sold at profit. This not only massively increased the amount of food that could be grown in the area, but perhaps more importantly, it lowered the average relative cost of food for the locals (leading to a population boom relative to it's historical carrying-capacity).

Your poor marshy lands were perhaps historically a similar calorie-bottleneck.

Rice is maybe the most likely candidate for improvement here. Poorly-adapted varieties and/or a lack of technological know-how may have kept yields at a subsistence level for centuries. Perhaps a cross-breeding of high-yield foreign varieties (which don't grow well there) with a low-yield local variety (which does grow well there) had finally yielded a medium/high-yield variety that thrives in the local soils and climate. Maybe this change happened at the same time as high-investment farming methods like rice-paddies were introduced.

Suddenly, tons of marshy land not suitable for cash-crops becomes massively calorie-productive for the local populace. This calorie surplus allows more of the good land to be used on cash crops whilst the surplus rice becomes a commodity in and of itself. Populations boom as food becomes cheaper and more labor is freed from subsistence-farming toward specialized occupations. Zanclatis, once having been just one-of-many pitstops between Astras and Olynthaseia, now sees much-increased traffic as lower grain prices have made it a much more economically beneficial stop than it had been previously (with Diosidos and Nirossos growing into new pit-stops in their own right as Zaclatis becomes more-and-more congested). Meanwhile the lower costs of food (and increased labor pool) has made various ore deposits along the Sparteian Alps newly economical for mining causing Sozippa to become major hub along the highway from the mountains to Zanclatis.


Villages tend to explode in population because...

  1. Discovery of a local natural resource.
  2. The town becomes a center of trade (multiple trade routes, change in resources elsewhere).
  3. The town becomes strategically important (war, political maneuvering).
  4. Disease, disorder, etc. causes people/refugees to emigrate from other areas.
  5. Somebody important moves in (e.g., king builds a "summer palace" in the town), causing the regular courtiers, fans, sycophants, service providers, etc. to arrive. Examples include: palace, abbey/monastery, garrison (specific version of #3).
  6. One or more people become craftmasters (a specific version of #2).
  7. It becomes a "bedroom community" of a larger city nearby.
  • 3
    $\begingroup$ I'd say you maybe analyze the attached map and check which of the reasons can possibly apply. Say #7 is off since the question asks for major cities' growth, initially there is no larger city to be a growing suburb. $\endgroup$
    – Vesper
    Jul 10, 2023 at 9:12
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    $\begingroup$ @Vesper There's nothing stopping th OP from changing their map to meet the needs of one of my suggestions if that suggestion is found valuable. $\endgroup$
    – JBH
    Jul 10, 2023 at 16:55
  • $\begingroup$ Re: 1, or changing technology or legislation makes a local resource valuable, e.g. fracking, wind $\endgroup$
    – g s
    Jul 12, 2023 at 16:35
  • $\begingroup$ @gs You're correct, but it's still just a natural resource. Different resources likely have greater value at different times of a civilization's history due to technological and/or political development. $\endgroup$
    – JBH
    Jul 13, 2023 at 2:56


Your geology investigations of the peninsula were highly incomplete, as it was the norm in "early to mid Ottoman" both time wise and technology wise. Since there are already some cities where gold is found nearby, this is off, using coal is off by technology limits, and the other "sudden riches" that could attract that many people to an otherwise poor region that's only use is some level of maritime control over the northern route would be gems, any special resources available in your universe (magical, maybe), or some metals that hold great value in this time and place. Silver looks like the best of all possible findings of this sort. Having silver found would force local government to increase its army, and also allow to buy luxury stuff, more slaves, more tech, for example, to dry out some of the swamps for agriculture, as food would start to be very pricey with such city growth.

As an alternative, a global warming and an earthquake somewhere nearby would possibly raise the flatbed of the peninsula, making swamps drain by natural means and leaving fertile ground for agriculture, together with possible access to some delicious local plants or berries, so that a lot more people could feed off local lands, and overall these lands become a better place for living. Having a maritime route would allow influx of people, and local food abundance could allow natural population growth together with foreign.


A newly discovered resource or industry seems the most likely reason, during the industrial era of the 1700-1800s many cities developed within a few decades from what were previously small villages or towns due to strategic locations on transport links, canals etc, making factories there very worthwhile, or closeness to newly discovered natural resources (coal, iron, etc).

In the opposite direction, famine and natural disasters within the countryside and farms also often leads drought-struck farmers and workers to migrate to the cities in search for work, and can vastly inflate city populations during difficult times.

Depending on your world's history, a religious awakening could also bring an mass influx of pilgrims to the new "holy land" where the prophet was born, who then settle there over the centuries.

  • $\begingroup$ The first paragraph gives great examples, but also generalises further: A technological or social shift, happening over a broad geographical area, can make certain natural resources or geographical features much more important than they had been, causing especially rapid change in some particular place(s). $\endgroup$ Jul 10, 2023 at 18:51
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    $\begingroup$ Natural disasters can also include those that affect other cities. For a real-life example, Houston got an influx of population after nearby Galveston was devastated by a hurricane in 1900. $\endgroup$
    – dan04
    Jul 10, 2023 at 21:14
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    $\begingroup$ I notice that in the map, it looks like the penisula is close to the end of a long inlet, and that end is a small istmus separating it from another inlet from the opposing sea. Building a canal or even just an efficient portage across that inlet would be almost certain massive growth for those that controlled it. Look at how much wealth flows through the Suez and Panama canals, or what the Erie canal did for the economy of the US and Canada. $\endgroup$ Jul 11, 2023 at 2:49
  • 1
    $\begingroup$ @PaulSinclair There's no isthmus there, it's inspired by the Bosphorus and it's where the capitol of the Aurean Dominate is $\endgroup$ Jul 11, 2023 at 14:38
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    $\begingroup$ @TheWeaselSagas - sorry, I've never seen a map before that used green to represent water, and blue to represent land. $\endgroup$ Jul 11, 2023 at 17:04

To Answering the Actual Question: Trade

While other answers demonstrate reasons why a town or group of towns might suddenly grow, the OP has asked for the most likely reason based on his setup. The sudden discovery of a new resource/technology, population dislocation from a war/disease/famine, and cultural outcomes from things like religion are all common reasons for a population boom, but these are all things that can happen anywhere, regardless of geography. That said, there is one detail in the question that stands out as a reason why THIS region would spontaneously grow very quickly:

...for most of its history, little more than a stopover point for ships making voyages between the Capitol to the southwest and the gold-rich mountains of Monsaltu to the east...

Towns that sit on major trade networks have a tendency to becoming very large very quickly. What you normally see with these "stop-over" towns is that they start off as places that merchants pass through on thier way to where they are going, but imagine if you are a merchant, and you got 1/2 of the way to where you were going, and you found someone willing to buy what you are selling, and sell you what you are buying. You just cut your route in half; so, even if your total profit is a bit smaller, the time saved is both a major convivence, and increases your profit over time.

The difference is made up by locals buying and selling products from either direction that they do not specifically need, but that they are able to resell at a profit. Tolls can also be used to fleece passing merchants and encourage them to make your town thier last stop, and/or to profit from anyone who wants to make the whole journey anyway. These factors causes a massive influx of money to the region for very little work allowing entrepreneurs to quickly rise up to positions of great wealth.

These entrepreneurs will want to capitalize on thier excess income by investing in new local businesses. These businesses create jobs pushing up the cost of labor, and the town's position as a trade center means that there are lots of things available for sale. All of these factors work together to make it a popular place to immigrate to because people from near by areas know that they can earn more money, and have the option to buy more goods and services by living here.

Orchards could be another good reason.

Most crops, if destroyed or neglected, can take anywhere from a few months to a year to replace. But fruit baring trees like your coconut, olive, and citrus trees take on average about 5 years to even start producing fruit, and don't get up to "mature" production levels until they are 10-15 years old.

So when a region becomes unstable, orchards become a much more difficult food source to maintain and replace than annual crops like wheat, beans, squash, etc. So, the value of these crop goes way up, and can stay up for a pretty long time because wise farmers only plant orchards during times of peace.

Historically, this was seen as the biggest factor in the rise of Rome. The Eastern Mediterranean lost all of its olive orchards as the region became embroiled in generations of constant warfare; so Rome, which started off as just a small olive growing community, was able to make a massive profit selling olive oil to the waring Hellenistic Kingdoms, and from here, it did not take long for Rome to grow from a small Etruscan colony to become the largest and most powerful city in the ancient world.

Likewise, if a nearby area were to fall into an unstable condition, your region could leverage its already existent orchards to supply the area with over-priced tree fruit products.


New Technology

Other answers mentioned discovery of a new natural resource. Similarly, the emergence of some new technologies may make extracting natural resources suddenly much more possible or profitable. For example:

New farming techniques

Without refrigeration and bulk transportation, any given region can only support as much population as the local countryside can produce food, no matter how desirable an area it may be otherwise. Advanced irrigation can dry out wetlands or deliver water to arid lands, potentially turning otherwise-uninhabitable areas to breadbaskets (think California). Irrigation canals are as old as history, but Archimedes' screw, which enabled pumping irrigation to higher elevation, is a game-changer and about the right technological level for your society. Beyond irrigation, they could develop new types of fertilizer or discover/breed new crops well-adapted to the local ecology.

New mining or refining technology

Advanced steel alloys and explosives can enable mining in harder rock. Improved smelting or chemical purification techniques can make it newly profitable to mine ores that contain high levels of some desired material but also some contaminants that were previously too difficult to separate efficiently.


canned peaches Effective Range

Like a few people here I lean toward a variant on trade route outcomes, in this case effective range of vessels.

Your peninsula is halfwayish, or whatever figure is plausible for the distance, between point A and B. That's not particularly special.

Ships require sailors, sailors require food. More food means less cargo, or more cargo and frequent stops.

Travelling all the way from A to B requires 5-6 stopovers, or some terrible cases of scurvy from the heavily salted rations.

Fortunately a poor-tasting syrup has been developed, which be used as a bulk preservative for fruits.

This JUST makes it possible to cram enough food in to just about get a full ship with crew to point B with a single stopover.

The peninsula is the lucky recipient of any ship wealthy enough to invest in the healthiest possible ratio of cargo:time:starvation.

The other stopovers aren't so lucky.

There have been similar towns spring up because they were placed at the limit of a steam engine's effective range. They just have to grow enough to remain relevant once technology marches on again.

The food preservatives are an idea I like as they're not directly linked to trade, the shipping benefits as a side effect, but any development affecting range is suitable.


An option which is not dependent on migration: Higher fertility, lower mortality

Maybe they’ve discovered germ theory and use it to drastically reduce childbirth mortality and mortality from contaminated drinking water.

Maybe they’ve found ways to produce more food or food with more nutrients, leading to less starvation and healthier children and women.

Maybe there is a change in culture or religion which makes having (unprotected) sex and having more children more desirable.

Maybe they’ve discovered vaccines, or antibiotics or mosquito nets (to protect against malaria) or any other invention which will drastically improve health and reduce mortality.

Note that population growth is exponential. Even just increasing the average number of healthy offspring from 3 to 3.5 per woman will have a huge impact after a few generations.



This is the one answer I haven't seen yet suggested, but what about religious motivations? Maybe your empire is currently going through a period of significant religious change driven by an influential prophet or several and there is some prophesy or similar linked to the peninsula. Maybe (one of) the prophet(s) said everyone is blessed in the afterlife who drank water from a local river or lake. Maybe there's a prophecy that claims it will trigger once great cities are built on the peninsula.


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