Ambassador:
The King will not personally be able to spend much if any time in foreign territories, so he will need to appoint others to watch what happens there for him. Even if a foreign power has declared themselves hostile to your civilization ambassadors will not be attacked by city guards on sight, as would other players. This doesn't mean they're safe, but it does mean someone will have to deliberately attack them. Ambassadors and the King may communicate by automatic messenger (with appropriate travel delays between the time the message is sent and the time the messenger makes it back to the King) or by player character messengers. Enterprising diplomatic service personnel will find it to their advantage to develop a technique for sending coded messages. I think it is key that features like this not be programmed into the game. Make it possible, and useful for players to come up with their own techniques in all aspects of the game and a great variety of them will come about. What's more fun, being the guy who reached fortieth level, or the guy who created the gameworld's most popular message encoding system? A critical capability for ambassadors will be translation. Ambassadors will either need to know the language of the territory they are visiting, or will need to hire player character translators that do.
Public Works Officer:
Territories may be developed, new buildings constructed, city walls erected and bridges built. The King is unlikely to be skilled in engineering so he will need to hire player characters who are to make improvements. The Public Works Officer may or may not be an engineer himself. He is responsible for hiring those who will build improvements, and depending on the temperment of the king, may have a regular budget and the discretion to decide which improvements to build. At the very least he selects an engineer, turns funds over to him for compensation and construction cost and relays the kings instructions if any. This office is simply a title. There is no guarantee that the character will perform his duties faithfully, much less intelligently. This is why relationships will matter so much more in this game than in any other MMORPG. This character could take the kings money and jump a ship for the next kingdom, or help finance a coup. The King could then declare him an outlaw, and perhaps send players after him to kill him. The key to power in this game, unlike others, is in working with others toward your goals. A King's primary difficulty is going to be in finding competent, loyal players to work with.
Captain of the Guard
Somewhere between a chief of police and a militia commander, the Captain of the Guard receives funds from the King and uses them to recruit guards (NPC's) and equip them. The Captain of the Guard stations his men around the city and countryside, to capture thieves, kill outlaws and skirmish with raiders. The Captain of the Guard possesses the ability to pardon outlaws, just as the King does. He may also declare a player character an outlaw. This is normally results in characters going into exile, or hiding, but can very well result in their death.
Intelligence Officer:
The Intelligence Officer is the King's spymaster. He recruits spies, making sure they possess the foreign language abilities necessary for their job, provides them with the clothing native to the region they are to infiltrate, and trains them for their tasks. He, usually indirectly, watches the movements and activities of foreign ambassadors and rulers, keeps track of foreign armies and attempts to root out enemy spies.
Military Intelligence Officer:
The Military Intelligence Officer recruits and trains subordinates to infiltrate foreign cities and learn all possible about their military capabilities. He tries to discover troop numbers, the location and nature of fortifications, and the equipment provided for enemy soldiers. A good one will make every effort to observe foreign military exercises so as to learn enemy tactics, and weaknesses.
Lieutenant:
The lowest ranking officers in any military, with a couple of levels between themselves and the general. Lieutenants take direct control of small numbers of soldiers (NPC's) and maneuver them in battle. Lieutenants in charge of archers may move to position their squads on hills or follow up footsoldiers, while those leading cavalry or infantry will seek advantageous ground and routes of advance for their troops. The command and leadership skills of the Lieutenant will affect the morale of his subordinates and can be a crucial factor in battle.
Supply Officer:
Armies require weapons, armor and horses. The Supply Officer is given funds and orders to seek out appropriate equipment of uniform quality and type in amounts necessary to outfit whole units. The Supply Officer would do well to become very close to the craftsmen of the region, as NPC merchants cannot supply the numbers of items necessary, nor anything particularly unusual or high quality. The capabilities of the player character craftsmen of the civilization will directly influence the military's strength. The military will be a good source of income and practice for the smiths of the land. Supply Officers serve the Captain of the Guard as well.
Journalism
This is a setting in which humans are the means of transporting information, and therefore, the limit to the rate of human travel is the limit to the speed of communication. Players are going to be wondering, is Syracuse flourishing under the rule of its leaders? Who leads the city? What policies have been carried out, what people are important there, what do the citizens think of their home? No one unwilling to travel constantly will know unless they are told. There will be money to make in reporting. If players trust the information you provide, and there will be plenty of liars no doubt, then your ability to document and describe items of interest becomes very valuable. Players should be able to create letters, books, and notes as inventory items and then pay scribes to recopy them. These could be sold around the Mediterranean, and translators would find a purpose here as well. Propogandist will find ways to keep their stomachs full too I imagine.
Crafting
People are going to want to buy a wide variety of items and someone will have to produce them. A completely player driven economy seems a little foolish to me, as the players are the exceptions in the world. No one wants to play the guy making ugly clothing, but the setting has a use for ugly clothing. Leave NPC's to make basic items and players to create the distinctive. No doubt a blacksmith setup was quite expensive for commoners in this time period. An apprenticeship system would likely develop. The wealthy in assets blacksmiths, armorers, and weaponsmiths, maybe even shipwrights, would take on workers and instruct them in return for part of the value of selling the products of their labors. The instruction skill will play a key role in this. A more experience character may assist in the performance of a task and thereby improve the helped characters chance to increase his skill level through performing the action. The crafters will make money, provide a varied economy and provide some of the distinctive features of their society, such as the type of armors and weapons wielded by guards and soldiers.
Farmers
At the very base of the economy lies food. Food must be produced in order for the populace to survive, and a faction which is not producing enough food will find their background NPC population (key to the economics equations) shrinking. Every character, and NPC, will lose a a small amount of wealth a day in food cost. These funds will go into a pool which will be distributed to the owners of working farms based on productivity. Farm ownership will create a class of nobles in some civilizations, a strong government treasury in those that allow no private ownership of fertile land, and a large middle class in those that find large numbers of small lots being worked. Each region will possess a limited amount of fertile land, broken up into small lots. Players will be able to purchase land, both of the fertile type and lots for other uses in the city, by clicking on it and paying the listed price to the current owner. Each farm lot must be worked by NPC farmers, which you hire for the going rate. Farms will be destructible, so you might also want to hire NPC guards. In war, farms will be a prime target, particularly those of a city which has not built a granary. Farming will not be a specialty of action, but will guide player actions in other areas. Owning working farms will be a goal of many players, and the limited number of possible owners will lead to scheming, negotiating and conflict.
Merchants
The apprenticeship system, and the obstacles to travel will insure that their is great variety in the goods produced in different regions of the Mediterranean. After acquiring capital, some players will find they can make a great deal of coin by transporting goods and selling them where they are scarce. Some merchants will work with farmers. Surplus farm production will pile up in a cities granary, if one has been built, and merchants may buy it and take it to a city with too little food being produced to support the population. NPC's die off first when there are food shortages, but if it gets bad enough even player character can suffer. Characters who should have died in real life, will in this game wake up very weak, and healing times will be much slower than in most games so injuries aren't taken lightly, in the local equivalent of a hospital. If player characters are starving an invading force will find little resistance. It seems likely situations will arise where a city has grown far too large for the local harvest and through military or economic power feeds its citizens with the produce of a foreign region, much like Rome's need of exports from north africa.
Mercenaries and Soldiers
There are always uses for people with weapons. Player characters soldiers could be used to supplement primarily NPC armies. Competent assassins will be much sought after individuals, as players killed do not permanently die, but do lose any current titles, including King. Most guards will be NPC's, but some will look for the particular skills, specialties and intelligence only a player character can provide. NPC guards will work like inventory items. Purchase a guard and he goes into your inventory. Drop him where you need him and give him an order. Guards will be most useful if they are able to guard player owned land, attacking any trespasser. It would also be nice if they could guard players, following them and attacking anyone in combat with the player. The daily cost of hiring each guard will change with the local conditions. There will be a percentage of the NPC populace available to work as guards. Depending on the percentage currently employed, the price will go up or down. Guards will work on a two week contract so that each two weeks they will adjust their prices based on the current market conditions and you may choose to fire them if the prices have jumped too high.
Horse Breeders and Horse Thieves
The programming necessary for this would probably be the first cut (along with a naval environment), but horses with specific traits, and the ability to reproduce in time would add an interesting extra level of complexity to the game. Varied statistics for speed, endurance, toughness, appearance, age and sex would mean that some horses would be more sought after than others, and militaries would have cavalry with distinctive characteristics based upon the local breed. With enough statistics you would have constantly evolving populations of potentially huge value. If two horses of opposite sex are left together on the same lot, with food and enough time away from work, they reproduce and the new horse possesses characteristics derived from its parents. Good breeding horses would be an important commodity. The breeder would have to purchase and pay maintainence cost for enough land to support the desired number of horses as well as guards to protect them, particularly for when he's away offline. You might wind up with an in game equivalent of Numidian Cavalry and mercenary units forming and selling themselves and their mounts to the highest bidder.
Engineer
Thief
Spy
Teacher
Miner