OK so lately ive been playing and I will be winning the tech race at the beginning. I will get mansonry, then irrigation first, maybe even code of laws and currency(which i like to tech to get the free market). And I will notice that my opponent (h2h) is way behind. I have seen them be at 2 techs, when Im at 8 or 9, then all of the sudden the next turn, they will have 11 or 12 techs. How is this possible? I understand backfilling, but I dont understand how they could be getting all these techs? I have seen it happen to me against multiple civs, so its not civ specific. I want to know what they are doing so I can do it. I have done something similiar with the chines on a couple of occasions. I would build settlers(one grassland two forests) with every new city, including the first city, waiting until all but one of the first tier techs are teched, then tech the one that hasnt been teched, and I would backfill all the first tier techs, and with writing would then get literacy, and be on my way to code of laws. I have to assume its something similiar to this, but I dont understand how they are doing so late in the game. Can someone explain to me how they are doing it and give an example so I can try it myself?