After finally building the needed Arsenal, I was able to take the decision to improve my heavy infantry. I am playing Judea.
I had been able to build heavy infantry inevery province where I had a training ground.
However, when I tried to build some heavy infantry, the display told me I needed a barracks to build them.
As Judea, I have never had the opportunity to build a barracks, even though I have a number of training grounds. Judea does have a Zealot barracks, a unique building that enables the building of Zealots, who are medium infantry, but it does not enable the building of heavy infantry.
Despite this, my existing heavy infantry are converting to the improved version of heavy infantry, but I still cannot build any, and I still cannot build any barracks.
Is this intentional, or a bug?