I recently completed this. Prosperity was 100, Security 81.
The key is this, with the amount of trade Denarii you can make, my final funds being 41 short of 55,000 you can buy off the raiders, which takes care of that.
The next thing is the city walls effect, which only applies to Equite and Patrician housing. Therefore, I sited my pleb housing above the water pool and used the mass farmland there to produce wool and olives for Rome, along with grain and vegetables and placed the walled in housing bellow the pool with its farms to the left above the water there.
Below that, and right of the sand pits, I placed a large glass industry followed by an oil industry with trade docks far right of them. Those two trade docks along with the oil exports depot (Cyren) supply the exotic goods.
One other thing. I cut both those housing off from one another by deleting connecting roads and any pre-placed damaged buildings from the map.
To reduce unemployment, I placed 3 armour workshops (none of which had access to wool which I stockpiled for requests), which I mothballed on and off as needed.
You should not have stockpiled the food, simply place a lot of farms and more granaries to hold it.
Two helpful ways to raise security:
1 Place a Balista, a courthouse.
2 Place a forum, that way you can see your ratings when you click on it.
Also have three Jupiter temples, which you will need anyway.
[This message has been edited by lisa1212 (edited 07-08-2020 @ 04:15 PM).]