The Thracian said:
How Do i avoid my cities becoming Stagant
Stagnant means that there is not enough food for your city to grow any more. You need 2 food per population point. (thus a city with population 4 needs 8 food). You automatically get 2 food from the city itself, and the rest comes from working the land. If your city is stagnant, one of 3 things is happening:
1) You don't produce enough food. Solution: Build farms
2) You're citizens are unhappy. Each

is a citizen that still eats 2 food but DOES NOT WORK, even for his own food. Thus you are dragging him along with no benefit. Solution: Increase happiness with buildings (temples, colloseums, theatres) or Luxury Resources (spices, gold, silver, gems, dye, etc.)
3) Your citizens are unhealthy. Each

is a citizen that is "sick". Sick citizens still work, but consume 3 food instead of 2. Thus, you are wasting food. Solution: Increase health with food options (more varieties of food resources like corn, cow, clams, fish, wheat, etc.) and health buildings (granary, aqueduct, hospital, grocer, etc.)
If all of these things have been done, than you may have maxed out the particular city. Most cities seem to cap out at 16-18 population; a fully farmed city tends to cap out at 24-28 population, but a very poor city site may only net you 10-12 population or worse. Choose the land where you build cities carefully.