The agora was not only the social but the economic heart of ancient Greek cities, so in my own game I have it give +2 culture and +50% tax output. In Hellenistic Kingdoms, an agora must be built before a gymnasium, temple, theater, etc. In a Roman game, I would make the same requirements of the forum. Here is the Civpedia description I wrote up for Hellenistic Kingdoms:
#BLDG_Agora
^
^
^The [Agora] produces a 50% tax output in its city.
#DESC_BLDG_Agora
^
^
^A large, open public space which served as a place for
assembly of the citizens and, hence, the political, civic,
religious and commercial center of a Greek city. Buildings
for all of these various purposes were constructed as needed
in and around the agora. Formal layout of the agora was
developed in the Hellenistic period. The Greek agora is the
predecessor of the fora of imperial Rome.
^The Agora of Athens was occupied without interruption in all
periods of the city's history. It was used as a residential
and burial area as early as the Late Neolithic period (3000
B.C.E). Early in the 6th century, in the time of Solon, the
Agora became a public area.
^But the agora was not unique to Athens. It was central to
every Greek city, serving as both a marketplace and meeting
place. It was a large, usually rectangular space surrounded
by buildings. Platforms, altars and statues of gods, sportsmen
and political figures could also be found there. The stoa,
which formed an edge of the agora, was a long building with
columns. Shops were located in the stoa. More expensive items
could be bought here.
^In some cities, local councils met in nearby buildings; other
buildings were used to store public records and important political
documents. Public spectators could watch criminals being placed on
trial in the agora. Men and slaves usually did the shopping, with
slaves and donkeys carrying the purchases; wealthier women may have
visited to buy perfumes, jewellery and expensive cloth. Farmers came
with their produce. In the large empty space of the agora, stallholders
set up their sun shaded tables and sold such items as meat, fish, fruits
and vegetables, cheeses, eggs, honey, wine, olive oil and animals (e.g.
donkeys, horses, hens). Fresh meat and fish were displayed on marble
slabs that kept the food cool. "Fast food" was also sold to hungry and
thirsty shoppers. Slaves were placed on display and bought and sold.
Merchants also bought and sold exotic foreign items in the agora.
Ivory and gems came from Egypt, elephants from India, silk from China,
wool from countries surrounding Greece, purple dye from the eastern
countries, grain from areas around the Black Sea. Craftsmen had stalls,
shops or workshops in or near the agora. Here they sold their goods or
took orders. Sandles could be measured and made, barbers would trim hair
and beards. Money changers and bankers would also conduct their business
here.
