Was messing around last night as I could not find accurate information on the great wall and found it can be VERY powerful. You can start using builders to build them during masonry and not after Renaissance. For building the wall it has to be on the border of your city and you cannot make a circle with it. A wall cannot enclose a space is I guess the best way to put it. If you have a single piece of wall you gain no benefit. If you have 2 pieces of wall then each tile will produce +1 gold if worked If you have 3 pieces of wall each end tile will produce +1 gold and the center one will produce +2 This is described in the wiki as each adjacent piece of wall provides +1 gold. I would not build the wall for this benefit unless I really needed the money or in preparation for the next and most powerful part. The Castles technology is easy to reach. When you do so each adjacent wall provides +1 culture. What this means is with a settler and 5 builder builds I can in 5 turns of making a new city create a city that if the 5 wall tiles are worked will provide +8 culture. Of if 3 tiles are worked provides +6 culture. This is a very large culture hit quite early and with 4 settler and 5 builders I can quickly produce 4 3 pop cities that together provide a whopping +24 culture and provide a significant boost through the civics tree. What was missing was the clear information on tourism. When flight is discovered all culture based resource improvements (i.e great wall) provide tourism. In the case of the great wall it is +1 tourism per adjacent piece of wall. Therefore at flight my +24 culture cluster would provide +24 tourism as well. If I had built a single city and managed to extend its border to the maximum and used 6 builders and had the population fed in to get it high enough the maximum limit would be +44 culture and +44 tourism. Anyone that is experienced knows this is a theoretical limit and I CBA work out the realistic ATM. Anyone experienced will also appreciate that the +44 culture boost is massive, mega. The +44 tourism is OK but only can be doubled with computers, but naturally still affected by trade bonuses. One small thing - Great wall tiles cannot be destroyed by builders but must be "replaced" with another build like an aqueduct or campus.