No Trebuchets?

Playing Byz in Early, I built a siege engineer's guild in the early 1100s, which I thought would give me the ability to build Trebuchets. No dice. I went on to build a Master engineer, which gives me Mangonels, but still no Trebs. What's the deal? [playing MTW-VI 2.01, BTW]

Trebuchets didn't exceed other war engines in energy and accuracy until the 13th century.

Right. I don't believe they become available until the High period starts in 1205.

Ok, then. Thanks, y'all!