A bit unclear exactly what you mean by "syll" and where it is embedded, but in our house, where there are concrete floors in the basement and first floor, they had placed wooden beams throughout the concrete where partition walls and door holes were later built. Likely to have something to attach door frames and partition walls to. In places where the wood was painted with lime or silicate paint, it held up, but where it was built in, it was rotten. For example, around the door opening to our pantry, the beam above the door survived, but the beam under the threshold was turned into "earth-like" crumbs. 