Barb Galleys use UNITAI_ATTACK_SEA and thus require their own AI function CvUnitAI::AI_barbAttackSeaMove(). Obviously, you won't find any AI_attackCity or AI_targetCity calls in there, as boats are only allowed to attack units outside cities. Also, there aren't any similar NumCities-thresholds implemented here and the AreaAI of their area (= water!) has no effect. So once they are around, they will check their valid options in the following order: flip a coin (50% chance) and -if lucky- check whether an improvement can be pillaged this turn (AI_pillageRange(iRange=1)) --> they will move onto Fishing Boats in adjacent tiles and pillage them . check whether an enemy unit can be attacked on this or on the next turn (AI_anyAttack(iRange=2, iOddsThreshold=25)) --> they will target your Work Boats 4 tiles away; this can be exploited to keep them away from your improvements by some nice disco-fox dancing or to lure them into the fishing grounds of your neighbors . check whether an improvement can be pillaged within 4 turns ((AI_pillageRange(iRange=4)) --> they will use their advanced AI radar to spot your improvements 7 tiles away , however, this radar can only detect improvements in the fog, if they exist for more than 20 turns (improved knowledge!, 5 turns for land units and improvements on land); the closest improvement "wins" (max(pillageValue/pathTurns)) . AI_heal() . AI_patrol() --> move into a random adjacent tile (iValue = 1...10,000); prefer unowned tiles (+20,000) and tiles not adjacent to borders (+10,000); if movement points left, recalculate ALL options (if the patrol-move reveals a "fresh" improvement, that was hidden from the AI radar in the fog before, option 3 will now be enabled and the respective mission (AI_pillageRange(iRange=4)) will be pushed) At what time will the game spawn barb Galleys? the era of barb animals must be over (NumCities >= 3/2*NumPlayers; GameTurns > Handicap.BarbarianCreationTurnsElapsed * GameSpeed.BarbPercent) the barbs must know Sailing How do barbs acquire their techs? Their real research rate is almost guaranteed to be 0, since they aren't allowed to have a Palace (8 commerce) and thus suffer from high maintenance (but they don't lose units via STRIKE). So they merely receive the 1 free beaker everybody gets (BASE_RESEARCH_RATE) for their current research plus 3% (BARBARIAN_FREE_TECH_PERCENT) of the cost of a tech scaled by the percentage of players who know it for each technology each turn. Hence, if the majority of the players in the game knows Sailing, it won't be long until the first barb Galleys come visit your fishing grounds.