Mechanics

A city that rebuilds its own services every month

Caesar steps its whole city in 106 steps a month: a hundred one-row passes in which houses climb and fall, then a rebuild of land value, water and every service flag from scratch. Houses react to last month's services, so a city grows about a month behind the buildings that cause it. This is the model under the Housing page: where a house's land value, its needs and its unrest come from.

Applies to Caesar

One month is 106 steps

The executable counts a month in steps. The first hundred of them, steps 0 to 99, each run the housing pass over one row of the 100 × 100 map: step n develops every house whose anchor tile is in row n. The last six do the bookkeeping. Step 100 resets the service layers. Step 101 counts the population, traces the water, and runs four small economy routines whose results become next month's inputs. Steps 102 to 105 each rescan one quarter of the map's rows (0, 25, 50 and 75) and lay every building's effect back down. After step 105 the month counter advances; every twelfth month the year turns and the year's accounts are settled (see the industry and taxes page).

Because the services are rebuilt at the end of one month and the houses are developed during the next, a house always reacts to last month's services. Building a market does nothing for the houses beside it until the month after the scan that next finds it.

Services are rebuilt from nothing

Step 100 clears the whole land-value layer to zero and clears every service flag except two bits the Forum's walkers leave. Land value is then rebuilt by the four scans, each building adding its effect to the cells around it. The effect is a square (Chebyshev) radius: a radius of 3 covers a 7 × 7 block. Each source has three numbers: how much it adds, how far, and a ceiling.

The ceilings are why the manual's sentence "when an area is under the effect of two or more different limitations, the lowest limit applies" is literally true. Every cell keeps a running minimum of the ceilings of all the sources that reached it during the scan, and its land value is clamped to that. A heavy industry's ceiling of 2 caps every other building's effect within four tiles of it, however many temples are there. Land value has no lower clamp either: rubble and low houses can push it below zero, and the Maps panel has colours for −1 down to −4 and lower. The unrest layer, below, has no floor at all, and a real save holds −43 in it.

What each building adds around it

The figures are the original's, from its table of service handlers (one per tile id). Walls, towers, wells and reservoirs add nothing, as the manual lists.

Housing: Each house adds a base figure plus an offset that rises from −1 for the lowest grades to +2 for the highest, within 1 or 2 tiles; the two lowest groups of grades are capped at 4 and at 8. The base is recomputed every month from the tax rate and the unemployed share of the population, and was 2 in the real save checked. So in a healthy city every house adds to land value, and in a badly taxed or idle one the low grades subtract, which is how taxes and unemployment move land value.
Temple: Land value +1 within 2 tiles in its first four stages, within 3 in its last four. Unrest −2 within the same radius.
Forum: Land value +1 within 2, 3, 4 or 5 tiles by pair of grades. Its tax-collecting reach (the administration flag) is 6, 8, 10 or 12.
Bath Houses: When watered: land value +1 within 2 tiles, and the baths flag within 3.
Oracle: Land value +2 within 8 tiles. Unrest −2 within 5.
School, Hospital: Land value +1 within 3. The school-or-hospital flag within 4.
Prefecture: Land value +1 within 2, capped at 8. The administration flag within 4. Unrest −2 within 3.
Barracks: Land value +1 within 3, capped at 5. Unrest −3 within 5.
Theater, Coliseum, Hippodrome: Land value +1 within 3, 4 and 5 tiles. The entertainment flag within 4, 6 and 7.
Market: Land value +1 within 1 tile, capped at 16. The market flag within 6.
Workshop: Land value +1 within 3, capped at 3.
Heavy Industry: Land value +1 within 4, capped at 2: the lowest ceiling any building sets.
Working fountain: Land value +1 within 2 tiles, once it has water.
Rubble and burning buildings: Land value −2 within 3 tiles and −2 within 1, capped at 8. The only things that lower it, with the lowest house grades, as the manual says.
Road pieces and plazas: Within 1 tile. A plain straight or corner piece adds nothing, and paved as a plaza it adds +1. A T-junction adds +1 (+2 as a plaza) and a four-way crossing +2 (+3 as a plaza). Which tile ids are the junctions is a strong inference from their shapes. It is the manual's "simple roads" adding nothing, and "intersections ... raise land value slightly".
Wall gates: Tiles 0x94 and 0x95: land value +1 within 2, capped at 8, and unrest −2 within 2. The identification is a strong inference: it matches the manual's gates, "manned by local militia", which "raise land values slightly" and "set a limit on how high land values can rise around them".

The six needs, and where each comes from

The manual lists them "in order of importance: water supply, road access to a forum, nearby baths, nearby markets, nearby schools or hospitals, and sources of entertainment". That is exactly the order in which the housing routines test them, grade by grade, and the order of the Housing page's needs. The administration flag (Forum and Prefecture) is a seventh bit, used for taxes, not for housing.

Water: Wells reach 1 tile, reservoirs 3, and a working fountain 6. A fountain works only if a run of pipe reaches a reservoir, and the game flips fountains between working and dry, which is the manual's "alternate between filling and draining".
Road access to a forum: Carried by the Forum's own walkers, who mark the cells they pass; a Forum sends its walkers on a timer that shortens with grade (7, 6, 5, 5, 4, 3, 2, 2). A strong inference that this is the manual's "road access to a forum". The refresh that turns the walkers' mark into the flag runs only when the executable's 18-month counter is zero, which would mean a house can keep the flag well after its forum is gone; that consequence has not been observed.
Baths: Within 3 tiles of watered Bath Houses.
Market: Within 6 tiles of a Market.
School or hospital: Within 4 tiles of either.
Entertainment: Within 4, 6 or 7 tiles of a Theater, Coliseum or Hippodrome.

Unrest is a second layer

Land value is one of two layers a house reads. The other, which the Maps panel draws as "trouble areas" on houses, is unrest, and it is the one that can destroy a house. The lowest four grades collapse into rubble when unrest at their cell passes 20, 30, 40 or 48, and the collapse spawns a rioter and lowers the Peace rating by 2. Higher grades have no such test, which is the manual's "people living in tents and low-grade housing are more likely to riot".

Unrest is lowered by the buildings that calm people (temples, the Oracle, prefectures and barracks each subtract 2 or 3 around them) and raised by a monthly step over every house cell. That step adds a growth figure, which the economy routine computes from the population tax rate and the conscription rate, where the cell is inside a Forum's or Prefecture's administrative reach, and subtracts 2 where it is not, (plus or minus a small random draw), then clamps the cell to between −8 and +50. High taxes and conscription raise it. The manual adds unemployment to that list; in the executable the unemployed share acts through the base each house adds to land value instead.

What a house does with it

Once a month, for each house whose anchor is in the current row, the game runs the handler for that grade. It first checks the unrest collapse (the lowest grades only), then compares land value at the anchor with the grade's two thresholds, then checks the service flags. A missing need drops the house a grade whatever its land value; a satisfied one lets it climb if land value is above the next threshold and the city is big enough. The thresholds, flags and city sizes are on the Housing page, grade by grade.

Growth outward is the same pass. A house that climbs to a pair, a 2 × 2 or a 3 × 3 first checks that the cells it would swallow are open ground or houses of an equal or lower grade; a building of any other kind blocks it. Temples and Bath Houses use the same machinery with their own thresholds, which is why the manual says "temples act like houses".

Naming, and what has been checked

The layer this page calls land value is the one stored at 0x61F4 in a save, and unrest is the one at 0xB014. They are the names the original's own Maps panel gives them ("land value" and "trouble areas"), and since 2 October 2026 the Gaius source uses them too (its older notes and the research corpus still call the first "coverage" and the second "land value"). Checked against real saves: land value and every service flag over all 10,000 cells of fifteen of the seventeen saves (the other two were written between a month's steps), the water pass, and a whole month's houses, records and unrest across six consecutive saves a month or less apart. The housing handlers have no direct ground truth in saves that far apart, so they are pinned by tests of exact writes; and the random draws that move unrest between steps could not be checked, because a save keeps no generator state. Not covered here: the ratings, promotion, the Legion and its battles, and the plebs.