Every burgher family pays 6gp/season in taxes. In addition, every 125 burgher families provides one point of Fleet Support. Naval, logistical, and intelligence units have their support costs shown below:
Purchase price and support cost are fairly straightforward; the number of GP you must pay to construct the unit, and the number of points of Fleet Support required to sustain it. Logistical units can be allocated to three tasks: trade, transport, and supply. Trading generates income for the oligarchy. Transport allows ships to transport ground units (cavalry platoons and foot platoons take up the same amount of space, as cavalry platoons are half as large). Ships with marines have their marines levied, paid, and supplied by the burghers. Units conducting supply missions carry supplies to land units in the field; their ability to conduct supply operations is expressed in a range and a capacity, which is the number of companies that they can keep in supply at that range. You can double the range by halving the capacity, and visa versa, to a maximum of two doublings (so a 40-wagon caravan could supply 12 companies at a range of 60 miles or 6 companies at 120 miles, but not 3 companies at 240 miles). Only riverboats and longships can carry supplies up most rivers, while only caravans can carry supplies overland, and large ships may require a good harbor to unload efficiently. Further, cavalry requires four times as much supply as infantry, and siege weapons and special units may require more. This nicely models the strong historical preference for conducting operations along coastlines without introducing too much additional complexity - most domains are going to already want to have logistical units during peacetime for the trade income. If dealing with detailed supply is too much work, just reallocate sailing ships to cover the number of units you have in the field and don't worry about rivers, caravans, or supply distance; the important thing is that supplying troops reduces trade income (a lot).
Goon Squads, Spies, and Assassins are intelligence units. A goon squad is a gang of 1st-level thieves and assassins, suitable for petty mischief, breaking kneecaps, and kidnapping the children of influential persons. What they lack in subtlety and ability, they make up for in comic relief and expendability. A spy is a 4th-level thief who can infiltrate other estates, domains, and armies, provide intelligence to the burgomeister, and conduct sabotage. An assassin is a 4th-level assassin who can be used to off people. These units use the hijinks rules to accomplish effects instead of to make money. Details TBD.
While the burgh does support its own garrison, at a rate of 2gp/family/month, they're mostly constables and watchmen, not soldiers. One bowman per ten families mans the walls and can be called to arms, but the greater part of the fighting men of the city are the marines of the fleet. Depending on culture, marines might be a mix of hoplite-style heavy infantry and bowmen, reavers, or something else entirely. If the city finds itself under siege, constables and thieves may be pressed into service. Two constables can be mustered per ten families, and they are armed with clubs and shields and armored in leather. They're basically slightly-better militia. One first-level thief per ten families is willing to fight if circumstances are sufficiently dire (the other first-level thief per ten families has already skipped town). Thief units are expensive and fragile, but sneaky, and may be useful for sallying out against siege camps.
Constables: 2/4/6 Irregular Foot, AC3, HD 1-1, UHP 6, ML -1, 2 club 11+. Wages 3gp/mo.
Thieves: 2/4/6 Loose Foot, AC2, HD 1-2, UHP 4, ML 0, 2 short sword 10+, 2 javelin 10+. Wages 25gp/mo, can hide in shadows (deploy hidden at night or in cover), backstab for +2 to hit and +1 damage on a successful hit against disordered enemies or to flank or rear.
Finally, the total burgher population of the domain determines the class of its main market:
- <1000 families: Class VI
- 1000 families: Class V
- 2500 families: Class IV
- 10,000 families: Class III
- 25,000 families: Class II
- 150,000 families: Class I
Burgher events are probably mostly about money, markets, and hijinks. A merchant needs sponsorship to fund an expedition to a distant land, promising to share profits with his patrons. A sailor bears news of internal affairs in a nearby domain. A prominent nobleman borrowed money from the burghers but the harvest was poor, so he can't repay them, and the case is brought before the oligarchs (there's probably a whole slew of worthwhile "inter-estate conflict brought before the oligarchs" dilemma events, where favoring one side over the other influences loyalty). The city is unsanitary and there's a plague outbreak, killing some and sending others fleeing to the countryside (strengthening the other estates but weakening the burghers), or there's an economic boom or bad harvest and peasants migrate to the city from the countryside. A fire breaks out and ravages the city. Hurricane threatens navy. Vessel sunk in storm with hold full of gold. Prices of raw materials fluctuate, changing the prices or availability of goods. Trade shifts and trade income rises or falls for a season. Pirates begin attacking shipping. A famous bard, assassin, or thief moves to the city; could be a hench, could be a thorn in your side. A guild member is recognized as a master of his craft, providing an opportunity to recruit a skilled specialist. Weak burghers mean you have low-tier markets, which is penalty enough. Disloyal burghers evade taxes, burgle the treasury, burgle other estates, raise prices on all goods via predatory monopolies, provide intelligence to other domains, turn their ships to piracy or steal / "lose" their cargos, and try to have PCs assassinated.
Strategic locations relevant to the burghers might include areas with rich fishing (increased taxes or natural population growth), natural trade chokepoints like the mouths of major river systems (passive trade income as long as there's a sufficiently large burgher population there to control trade through the straights, pass, or river mouth), sources for rare trade goods (increased trade income), or sources of naval stores like pitch and timber (reduced shipbuilding costs).
Urban family surplus is only around 4gp/mo after garrison, urban upkeep, and all that stuff. We'll allocate 2gp/mo/family to taxes, and the other 2gp/mo to supporting fleet units. This yields 250gp/mo per 125 families. The amount of support that units need is based on the Merchant Ships and Caravans table on page 145, rounded a little. The trade income is also based off of that table, but it turns out to be about 100gp/mo of revenue per thousand stone of transport capacity. I did reduce this trade income by about 20%, with the assumption that the lost fraction is being taken by burgher captains and merchants and being ploughed into urban investment and their own private ships. Transport capacity is based on 200st per man, and marine capacity is likewise rounded a little. Supply is based on the value and volume of grain, assuming that food will be the primary requirement of an army on campaign ("An army moves on its stomach"). Grain is 1gp/8st, so if a unit requires 60gp/week in supplies, that's 240gp/month, is ~2000st of grain per month. A large sailing ship carries 30kst of cargo, so it can keep 15 companies of infantry in supply if it's making one delivery per month. Instead I've worked these numbers to reflect one trip per week, assuming that supply depots cannot be maintained by a mobile army. In a week, a large sailing ship with a navigator can move 720 miles (assuming a day to load and unload at each end and five days under sail). Since we're assuming round trips, that gives us a supply distance of 360 miles, and means it can keep 60 companies in supply (since it's carrying 15 company*months of grain on each weekly trip). Cavalry costs 4x as much supply, since most cavalry units have a supply cost of 240gp/wk instead of 60gp/wk.
The families for the various market classes have been reduced somewhat from ACKS' nominal figures, as a result of assumed-centralization and also to account for the shift of certain types of markets out to the other estates (church controls the market for divine spellcasting, tower controls the market for arcane spellcasting and sages).
This addresses some of my historical complaints about the thief domain game . Thieves retain their status as a "support" domain - they generate money, supply and transport armies, and gather intelligence, none of which are "primary strike" functions but all of which are necessary. Thieves win wars, and they do it without fighting. Pretty sneaky, eh? The thing here is that I have separated thief domain income from hijinks and crime. This opens up a broader range of playstyles for thief-domain PCs; a venturer can focus on trade and ignore hijinks altogether, while an assassin might only dabble in trade and keep a bunch of assassins on the payroll. It introduces real tradeoffs.
It also helps with suspension of disbelief. If trade generates a ton of money, that's reasonable and believable (maybe should add a chance of sinking for each vessel trading for each season, but meh). If thieves generate the same amount of money per unit time by blackmailing people, that's a little less believable.
Finally, by making ships easier for players to acquire and maintain (and by having Fleet Supply go to relative waste without them), hopefully ships would see more use, both for mid-level travel for adventure sites and for high-level naval battles. Since we want PCs to use ships for transport, we'd probably also want a rule that a ship performing Trade can carry a small number of characters without interfering with its trade mission - otherwise PCs will be loathe to use them, for fear of disrupting their cashflow.
Establishing burghers as the naval power also sets up the nice historical dichotomy between Athens and Sparta, Britain and France (and later Germany), and the US and Russia, of sea powers and land powers, depending on how you allocate your population.