How to protect untreated wood posts for 200 years?

I saw some guys on Youtube that were building a wilderness cabin and they were sticking the ends of all the logs into a fire to char them real good as a way to keep them
from rotting I presume.    I never saw that before....    Does anyone know how much if at all this practice is helpful to the longevity of the logs ?

I t would help. For sure.

But, it would depend on the dampness of the ground, the soil composition, wood species, the quality of the char, and what sort of ground the pole was planted in, and if there is vegetation growing against it.  

The things that rot or deteriorate the pole are going to be bacteria and fungi, mosses and lichens, or ants or termites, depending on what the local scene is.  

Most poles will rot out at or near the point of contact with the soil.  I've seen fences made from 100 year old fire killed western red cedar.  That is where they rotted.  

It sort of falls into the 'edge effect' phenomenon.  There is more diversity two different climates meet than in either of the two climates would have as added individuals.  

So, where air meets soil, where soil meets wood, where soil moisture meets wood, where plant moisture meets wood... that area usually rots first.  Reducing those factors, while using a more rot resistant or dense wood might be a major factor as well as planting the poles in rockier or sandier soil rather than silty or clayey soil is bound to have a more favorable condition.    

My experiences:  black locust wasn't really worth cutting and putting in, ( i didn't peel them and I heard that would have helped.)  We have cedar posts that have been in fences for 70+ years that are coming to the end of their useful life.  We have some osage orange corners we will dig out or pull up if we can and replace just because they are too short for the fences we are building now and I would look like an idiot to stretch a new fence from posts that were put in almost a century ago.  I'm in a dryer climate than many of you though.

I have tried charging on my raised beds. So far, so good.  I really don't have a big enough sample..nor have they been in place long enough.