Can anyone help me out please?

If a city defense (say one at 60% due to culture), and this is reduced (say, to 0) by bombardment, how and under which circumstances is it ever brought back up to its full strength?
Is defense due to culture and defense due to buildings treated the same way for this purpose?
thank you

It starts rebuilding after 1 turn of no bombardment. IIRC it's about 4% a turn, though I'm not sure about that last one

Hmn interesting, thank you. I have never actually seen it rebuild.

It's pretty easy to see, just bombard it to 0 and then stop for a couple turns. Happens to me all the time with naval wars where my destroyers or frigates are the first on hand to bombard a city's defenses while the transports/galleons are trailing behind with the actual invasion troops. I get the first city to 0% then move the DDs on to start on the next one, but by the time my transports get to the first city, its defenses have already gone back up to 4% or 6% or whatever. Also, I'm not sure if it's a static value increase, I think it has something to do with how much culture/turn the city is generating, or perhaps even the city's total culture, because I have definitely noticed that capitals tend to rebuild their defenses much more quickly if there's a lag in between my initial bombardment and when the ground troops actually arrive in a position to attack the city.