I wrote this text about 20 years ago for the now-defunct Tolkien gaming journal Other Hands. It deals with issue of city planning in a fantasy context.
Minas Tirith is a city planner’s nightmare—a big city on a hill with seven concentric walls and a very small number of gates (The outer wall has only one gate through which all traffic in and out of the city must pass.), which creates a serious logistical problem. Due to the lack of primary source references, my reasoning in the following paragraphs is speculative, though it is based on sound historical and military facts.
If we assume that the city has approximately 50,000 inhabitants—a realistic figure, given the size of Gondor—and that each of these consume 2.5 kg (6 lbs) of food per day (excluding water, which is supplied by internal wells and rain cisterns), the city must daily receive about 150 tonnes of food supplies. There would obviously need to be a steady stream of wagons coming into the city from the Harlond docks and the Anórien and Lebennin roads.
Assuming that one wagon can load 450-500 kg (about 1,000 lbs) of supplies, 300 wagons a day must reach the city, which makes approximately one every five minutes if the wagon traffic runs 24 hours a day. However, it seems unlikely that wagons would be working during night due to the absence of proper artificial lighting. Instead, it is more realistic to assume that the tempo is one wagon every two minutes. The roads running to Minas Tirith would clearly need at least two (and preferably three or four) lanes in order to be able to deal with this amount of traffic. Four lanes would certainly be necessary for the Harlond road.
The layout of Minas Tirith prevents the use of large wagons in the city. Instead, the city porters must use smaller and more agile carts, perhaps something similar to a hand-drawn rickshaw, in order to navigate the numerous tunnels and tight street curves. In ancient Rome, transportation of goods was only allowed during the dark hours to prevent congestion of the streets during the day-time. Most likely there were similar regulations in Minas Tirith. Outside the Great Gate there would have to be a reloading and storage depot area where goods could be transferred from wagons to carts. The wagons would arrive by day to deposit goods there and, after sunset, the city porters would come with their carts to take the goods inside the walls. One consequence of this arrangement is that the city’s bakeries and butcher shops should be located on the lowest level, preferably as close to the Great Gate as possible.
Another consequence is that the people running teamster and carting businesses should be influential in city politics; after all, their hard work ensure that the city stays well-fed. Most likely, the official overseeing the depot area is a senior “civil servant” who is appointed by the Steward and who reports directly to him.
It might be possible to have hoists on top of the walls to alleviate the congestion, but this would only be practical at the outermost city level, where flour sacks could be lifted straight from a wagon over the city wall to the backyard of a bakery. Such devices are not mentioned in The Return of the King, but it is likely that the Steward would have ordered their removal when the war approached in any case.
Every morning, a swarm of servants would have to descend from the upper city levels to buy fresh food. If there were a day-time city food market (very likely), it would probably be located in an open field just outside the Great Gate so that the peasants would not have to enter the city to sell their wares. There should also be a similar fish market right next to Harlond. In addition to foodstuffs, there would also be deliveries of raw materials to city artisans and the problem of transporting their products to other parts of Gondor, creating additional traffic through the Great Gate.
A big fortified city of medieval Europe had numerous gates in its outermost wall just to be able to deal with the transportation of goods. Medieval Visby in Sweden (a town much smaller than Minas Tirith) had three gates that opened onto the adjacent farmlands and a big port. Minas Tirith’s layout is clearly that of a fantasy world, making her an imposing beauty, though quite improbable.