In the following context:
“…but as the city has been losing functions it has been reasserting its most ancient one: a place where people come together, face-to-face.”
What does reasserting mean? I need to know this, otherwise, I would never understand the sentence. 
Hi again
Reassert is to go back to a former(usually high) standard and in this way to get back a reputation. A school for example might once have had a high reputation but over a period of time it may have gone downhill. A new headteacher could be appointed who wants to restore the school to its former high standard and in this way help the school to reassert itself.
Alan