Most of this data was obtained from a post made by SIM
to the Heavengames Forum. It has
all been common
knowledge, but SIM took the time and trouble to put it together in an easy-to-read
format.

At the end of every year, the game calculates a city's prosperity
level. This calculation is made as follows:

Let's say you have a city which contains:

50 small tents

100 Large Insulae

25 Grand Insulae

3 Luxury Palaces

The calculation would be:

(tents*5)+(large Insulae*65)+(G. Insulae* 80)+(L.Palaces* 1750)
----------------------------------------------------------------------------------
# tents + # Large Insulae + # Grand Insulae + # Luxury Palaces

or

(5 x 50) + (65 x 100) + (25 x 80) + (3 x 1750)
----------------------------------------------------------
50 + 100 + 25 + 3

or

14000/ 178 = 79

So let's say that last year your prosperity rating was 50. During this year
you have gotten your city up to the above levels.Therefore in January your prosperity
rating should be 79 right?

WRONG!!

You will get a two point increase. Then the following point adjustments
will be made:

Points are added if:

+2 Your city makes a profit. (Construction
not counted)

+1 10% or more of your
population lives in villas

+1 Less than 30%
of your population lives in tents or shacks.

+1 Active Hippodrome

+1 Less than 5% unemployment.

+1 People below Grand Insulae
have more than one type of food.

+1 You pay at least 2dn more
than Rome's min wage.

Points are deducted if:

-1 City loses money.

-1 Unemployment rate is
above 15%

-1 Your wages are below
Rome's

-3 You go broke and Caesar
bails you out.

-3 Failure to pay tribute

So your new prosperity level would be at most 60, and maybe less depending
upon how the above conditions applied to your city.