The techs under the keep (Fortified Villages, burning oil and the other one that reduces fire damage) suffer from an increase in their research time the more scholars you have garrisoned in the mosques / madrasa. I got to make their reserch take 40 min to finish with 21 scholars.
To replicate it you just need a Castle, mosques and a buch of scholars. Increasing the number of scholars garrisoned in the mosques results in an increase of research time to the 3 techs in the Castle. I was testing stuff out in a personalized game without any kind of opponents, with the resources set to the maximum, with the map revealed and starting from castle age.
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