I have been reading John Adams by David McCullough and was stumped by the expression of "erect galleries" as in the following excerpt.
In Massachusetts the idea of galleries for the public to watch the legislature was the custom. When Wilson of Pennsylvania, who agreed with him, moved that the doors be opened, galleries erected, or that Congress adjourn to some public building where the people might be accommodated, Adams enthusiastically seconded the motion, but to no avail.
What does 'erect galleries' mean here? I was guessing 'holding a constitutional session', but I am not 100% sure.