Help me flesh out my evil city for my 5e campaign, please.

[Spo]

Working on a homebrew where the PC's will be tracking down pirates/slavers that took beloved NPC's from the coastal town where the campaign began. After several adventures, the party winds up in city of Gateway, where the slaves were sold.

Some aspects of the city.

- Coastal city with an active port and high walls surrounding it. Arabian themed
- Large, multi-raced city.
- Slavery and trade brings vast wealth to the city.
- There is a sales tax on items sold openly
- law enforcement is very severe (no begging in the city; shanty towns/tent cities formed outside the walls/lot of one-handed beggars/pickpockets found here)
- there is a coliseum in there for gladiator type fun
- slave market and black market
- different tiers of brothels located within the city
- the captain of the guard is a minotaur
- several open markets
- there is a train system run by gnomes that takes purchased slaves and other merchandise down into the Underdark. The journey is long and ends near an underground ocean town where slaves are put aboard boats and shipped and transported to other regions in the Underdark (possibly a mindflayer island) and a large market place exists for creatures that don't like going topside to buy items (like drows). Also a slave market there as well.
- There is a palace in the center of the city surrounded by a moat filled with some type of beasts or creatures (maybe crocodiles?).

Now I need help fleshing out the rest. The goal is to have the PC's locate and rescue (buy back?) the NPC's found either in the city or in the Underdark.

Who should run the city? A single entity or a council?

How is order maintained within the walls. Patrols?

What are some of the laws in the city PC's should know when they enter. (maybe hey can hire a guide to tell them these things?)

Do they need papers to enter the city? Pay a toll?

What type of shrines temples should be there?

What about a curfew? Only registered persons (maybe wearing something unique) allowed after midnight?

Looking forward to your suggestions.

[Vogie]

Who should run the city? A single entity or a council?
A bit of both. In a very Roman style, a council of nobles with a single "first citizen" leader to break ties. This could also be a Dynasty, with a Matriarch or Patriarch on top, but everything is run by the same family.
Other massive-city-in-5e examples for reference:

In Waterdeep, they hide the identities of the council (called "masked lords"), save the one "open lord" that is the figurehead, to avoid any one individual being usurped or bribed.
In Ravnica, the 10 guilds have a tenuous relationship but overall function as a whole. The Azorius Senate care the most about the laws, so they seem to be in charge, but it is only able to do so at the behest of the other 10.


How is order maintained within the walls. Patrols?
It depends on how chaotic or respectful you want the city to be. Guards and/or a Watch are fairly common regardless of most things. You could have:

a moratorium on most weapons, requiring people to check them at the walls or as they enter buildings
required registration of weapons and spellbooks for those that enter the city, and Bracelets/Bracers of Less Harm supplied by the governing body to lock all innate casting to minimum damage.
everything allowed, but having an enchantment that allows the guard to detect offensive magic cast or fights breaking out, like a magic version of London's Shotspotter system
Other Examples:

In Waterdeep, the City Watch only wields clubs, and while there isn't a ban on open carry of weapons, adventurers that are heavily armed are often made note of and paid attention to. The Guards guard the walls, and the Watch watches everyone else.
On Ravnica, nearly everyone is armed in some form or fashion. Spellcasting is incredibly common, and the Wojek are the faction of the Boros that act as the "beat cops" on the streets. The Azorius also have Arresters that are a combination of Process Server and Corrections officers, but they rarely are on a periodic patrol.


What are some of the laws in the city PC's should know when they enter. (maybe hey can hire a guide to tell them these things?)
Do they need papers to enter the city? Pay a toll?
What about a curfew? Only registered persons (maybe wearing something unique) allowed after midnight?
These depend on the answers to your above questions. You don't want the sword-toting PCs to walk past the guards perfectly fine, then have them immediately arrested when they pull a sword 5 minutes later.

[DeTess]

Working on a homebrew where the PC's will be tracking down pirates/slavers that took beloved NPC's from the coastal town where the campaign began. After several adventures, the party winds up in city of Gateway, where the slaves were sold.

Some aspects of the city.

- Coastal city with an active port and high walls surrounding it. Arabian themed
- Large, multi-raced city.
- Slavery and trade brings vast wealth to the city.
- There is a sales tax on items sold openly
- law enforcement is very severe (no begging in the city; shanty towns/tent cities formed outside the walls/lot of one-handed beggars/pickpockets found here)
- there is a coliseum in there for gladiator type fun
- slave market and black market
- different tiers of brothels located within the city
- the captain of the guard is a minotaur
- several open markets
- there is a train system run by gnomes that takes purchased slaves and other merchandise down into the Underdark. The journey is long and ends near an underground ocean town where slaves are put aboard boats and shipped and transported to other regions in the Underdark (possibly a mindflayer island) and a large market place exists for creatures that don't like going topside to buy items (like drows). Also a slave market there as well.
- There is a palace in the center of the city surrounded by a moat filled with some type of beasts or creatures (maybe crocodiles?).'

Now I need help fleshing out the rest. The goal is to have the PC's locate and rescue (buy back?) the NPC's found either in the city or in the Underdark.

This sounds very interesting. One thing to keep in mind is just how 'evil' this city is. By today's standards everything to-do with slavery is wrong, but that hasn't always been the case in the past. The city could quite easily have a fairly Neutral bend while still facilitating the selling





Who should run the city? A single entity or a council?

Given that you've described this city as very multi-cultural, I can't really see it having a single tyrannical leader. This sounds like the kind of place that would have a city-council of sorts, maybe with representatives of the major merchant guilds, as 'fantasy-capitalism gone wild' would be an interesting way of flavoring a city like this in a Neutral way while still explaining the slavery and the like ('everything is for sale').



How is order maintained within the walls. Patrols?


If we're going with the Merchantocracy idea, maybe have different districts owned by the various guilds, or even rich individuals, who have their own mercenaries to keep order in their districts. This could even keep each district its own flavor ('Don't cause trouble in the harbor district, as the fishmonger's marines have regular patrols and will gut you', 'You can get away with almost every crime in Undertown, provided you've paid your crime-tax. If you haven't, the beggar-kings unseen watchers will make you regret it.).



What are some of the laws in the city PC's should know when they enter. (maybe hey can hire a guide to tell them these things?)

In the Merchantocracy, contracts would be enforced rigorously everywhere, and acts that interfere with business would be punished harshly (theft, vandalims, etc). Since things vary by districts, the players would be encouraged to actually hire a guide that can explain every district's idiosyncracies to them.



Do they need papers to enter the city? Pay a toll?

I think the players probably would have to get some papers that give details about who they are, what they can do and what they're worth, as such papers could be used by the various influential merchants to decide whether the PC's are worth dealing with or not. It could essentially be a combination of passport, credit-rating and letter of pedigree.



What type of shrines temples should be there?

There'probably be a major temple to a god of merchants, and smaller shrines to just about every god if you know where to find them.



What about a curfew? Only registered persons (maybe wearing something unique) allowed after midnight?


I don't think a city like this would have a city-wide curfew. There might be one in some districts, but for many others business would be 24/7. Districts that I could imagine having a curfew would be the banks and jewelers districts, and maybe some residential districts enforce a curfew for those without prove of living there.

[MoiMagnus]

- slave market and black market

Is the black market actually a black market (i.e illegal) or just a shady market where you can buy anything but actually approved by the governor/king/... of the city?



Who should run the city? A single entity or a council?

Some suggestions:
+ Efreets (so fire djins). It works well for the Arabian theme. (potentially too well)
+ A secret council: governors don't know the identity of each others, each one chose how he/she will pass this title at his death. Even the exact number of peoples in the council (or if the council actually exist) is a secret. Some high placed peoples in the hierarchy are public, and enforce the decisions of the council.
+ A group of mechanical entities, that continue long after the death of their creator to achieve their unique goal: making more money.



How is order maintained within the walls. Patrols?


It depends on the level of corruption you want.
+ Low corruption: Spies and Patrols. And "everyone will denounce you if you do something wrong". Denouncing illegal activities is highly rewarded. The suspect are captured and their mind is broken to magically check if they were indeed responsible. If not, the one who made a false accusation is subject to the same "torture" in order to find the other persons responsible (if any).
+ High corruption: Mafia. Order is maintained because some people have the monopoly on crimes. Every mafia/private militia sell protection against some stuffs (murder, thief, ...) and make sure nobody break those. They have agreement between each others to prevent it to routinely end up in a gang war (even though it still happens).



What are some of the laws in the city PC's should know when they enter. (maybe hey can hire a guide to tell them these things?)


"Don't pay attention to horrible stuff around you. Either it is approved and melding with it will kill you, either it wasn't and they will be killed for doing it. The first is the most likely. And NEVER try to free a slave or help someone, it is most likely a trap set up to condemn you to death. The most you can do is report a felony of a fleeing slave with this device (hand a blue necklace). And don't lose it, peoples will consider you as a slave if you do, disregard anything you say and report you as a fleeing slave. Blue is for strangers, Red for slave masters and other important peoples, Black is for people that work for others, like the patrols, White is for slaves, it has the symbol of its master on it, and if you see another colors... just hope you won't."



Do they need papers to enter the city? Pay a toll?


Yes to both. They need someone in the city to patronize them (Someone who will pay, or may be killed, if they break to much laws) hence a paper proving it.

They need to pay a toll for protection by the patrols, or pay the mafia for protection, or whatever, but they won't survive free very long without someone saying "they paid me for protection, so don't enslave them or I will take revenge".

Bonus: they need something to sell. Information, slaves, them-selves (as temporary gladiators or others), or proof that someone important requested their presence. You don't enter without reasons, tourism isn't a thing.



What type of shrines temples should be there?


Probably any temple that respect the rules "what happen inside isn't our matter, what happen outside isn't your".
But probably only "private temples", meaning that you need to know the good persons to actually get into a temple.



What about a curfew? Only registered persons (maybe wearing something unique) allowed after midnight?

This, or the city is never in "night more", and due to the different races, there is the same level of activity regardless of the hour.

[John Out West]

Something that I found interesting. I believe it was in Greek (Or maybe Roman) society that Masters would always have Beards while Slaves would always be clean shaven. This made it easier to distinct who was a slave and who was a free man. Slaves, of course, would be forcibly shaven, and this gets rid of the need for things like "Collars."

It brings up a fun possible dynamic as well, since most people would be unrecognizable without their beard and hair, you could potentially give your enemy a shave and a haircut and send them on a train to the underdark. Would be a fun way to end a campaign.