So we hear about ancient conquerors founding cities, and assuming they really are making a city "out of nothing", and it's not an embellishment, where they are said to found a pre-existing city, how exactly did they do it?
Edit Not that I'm necessarily interested in Alexander per se, but the scant knowledge I have of him is that many towns to this day bear his name, so they lasted, and also a number of cities with his name were large enough to leave discoverable archaeological remains, so he founded some successful cities (or at least, got his name on them).
From what little I know of Alexander, it seems that he was always on the march, conquering new lands and peoples, and founding cities here and there along the way. I would guess that, as a conquerer, he didn't have much time to invest in each little city he founded. I wonder what he actually did to found each city, whether it was more mythical-- just putting his name on an existing hamlet, or building an amphitheater in an existing cowtown, or it actually involved building some infrastructure in the middle of nowhere (a long-term, logistical and financial project), or getting a sizeable, self-sustaining population to migrate there and inhabit the city (a feat of politics and persuasion, for sure).
So that's what triggered my question, but I know of course cities were founded all over the ancient world, and any insight really into how this was done would be great
End Edit
So a city has buildings, roads, and other infrastructure, and one can see how a powerful and influential person could finance the construction of a city. But how do get people to move in and inhabit those buildings? How do you get a critical mass, to make it a going concern?
Did they just Build It, and People Came? Or did they have to recruit inhabitants from other places? Or did they perhaps just set up a marketplace, and farmers and herders started showing up, and then perhaps a judge and administrator to arbitrate disputes, and boom, that was it, a city?
There are many, many ways for a city to come about. Specific to your question, let's add in the element that 1) there is an identifiable founding leader 2) the founding into a city was intentional. Let's look into a couple of examples which cover this:
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A leader moulds an existing city in his image
This isn't a perfect fit, but it's worth mentioning because this kind of city was quite popular in Ancient Greece. Basically, a city would form (generally through synoecism) and trod along for a bit, developing most of the physical infrastructure and gathering the population. Then at some point in its history, a great leader comes around and reshapes the political, legal and social culture and strictures of the city in their image. Good examples of this are Solon of Athens and Lycurgus of Sparta. It's kinda cheating, but these kind of lawgivers were considered to be the founders of the city-spirit.
This kind of founding works by taking an existing city and founding new institutions.
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Settlers
A small group of people found a city that grows over time. The period of ancient greek colonization is a good example of this; the great city-states sent out a bunch of settler groups (usually at the guidance of the oracle of delphi). These settlers would set up small villages, using the skills and trades they brought with them. These then had the potential to grow over time; if the location was good, if they became a focal point of trade between the home city and new area, or because they enslaved a lot of people and built out that way.
Carthage is a decent example of this. It's got the epic founding story of Dido being exiled and sailing out to found a small village in a harbour in nowhere, Africa. A good location (and skill at ships) causes this city to grow.
These types of cities are intentional and often have a founding figure, but growth to actually being a city is slow.
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Military
The quickest and most efficient way to create a city: build a fort. You get these a lot along contentious borders. These are great. The military builds them, so it's done fast with military engineers and labour. The military garrisons them, so you've got a settled population for a while. If they stay long enough, then a civilian population builds up around them as people are attracted to the economic opportunity it provides.
A good example of this is Dara at the (Eastern) Roman/Persian border. This was founded by the Roman Emperor Anastasius as a base and refuge for troops at the contentious border. It had to be re-done by Justinian, but after that Roman/Persian conflict kept the area hot enough that there was almost always a garrison in residence. As the conflict consumed manpower, the city grew.
These types of cities are founded by and for the military for war, which bankrolls the establishment of general infrastructure and provides a starting population.
Note: I remember something about Russia trying to create a bunch of military settlements and that not going so well, but you'd have to research that yourself if you're interested, I don't know it that well.
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Land Grants
Basically, a person/organisation claims a bunch of land and parcels it out to people. This style of settlement-forming became quite popular in the Roman Republic/Empire. Basically, soldiers were promised a plot of land for farming upon ending their military career, they started running out of land, so the Senate used it as a way to found new settlements. This method was also pretty popular in early settlement of the USA and more generally during the European Colonization period, but someone else could tell you more about that.
To be fair, I'm kinda muddling two different types of city-founding here. One happens when there's a lot of migration pressure outwards. This was the case with the Ancient Romans; there were a lot of soldiers they owed land grants and needed to settle, and nowhere to settle them, so they made cities. This contrasts with eg: the Dutch East India Company, where they wanted to settle areas and used land grants as a form of bribe, to pull the population the wanted to the land they had. Sometimes these come together in harmony - New Zealand's Great Migration intersected the grand colonization plans of Edward Gibbon Wakefield with the overpopulation pressures of Britain's Industrial Revolution.
Overall, these cities are characterized by a large organization (generally a government or company) providing base infrastructure, then brining over a bunch of settlers at once. It's generally done in a fairly ordered fashion.
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Touching on some others
Here's some other types of founding I don't have as much to say on, for completeness: