I had researched all siege weapons from the ancient to medieval era and was using them regularly during sieges.  However once I hit the early modern I noticed siege weapons were unavailable to me.  At this point I had not researched siege cannons.  Once you hit early modern do you lose access to all ancient and medieval siege weapons?

Thanks. 

You lose ability to construct siege weapons upon entering industrial I think, maybe it is early modern, but yes you do lose access to siege weapon once you reach a certain era, no matter if you can build artillery or any other "wall destroyer".

When I was in industrial era I was unable to build siege weapons, I think I was able to build them in early modern but I'm sure I could not build them in industrial.

I thought they don't turn off until you specifically research mortar.

What this means is - in the past, you could build siege weapons on-site: you just need woods, ropes, etc. But once you get to cannons, you can't build those in the field. You have to build them in the city. So basically now you have permanent, but mobile siege weapons instead of temporary, but fixed location ones.

hmmmm....interesting