I just had an idea to tie together several things we discussed recently: the Nightfort, Craster, the role of the Blackgate, the recent reform of the Watch.
1) Both archaeology and history tell us that the Nightfort is the most ancient castle on the Wall. Probably the other castles were afterthoughts. Moreover, the Nightfort has the Black Gate as unique feature.
2) As Uncat suggested upthread, the Wall was once a separation between two worlds, with the Black Gate as the only mean of communication. It's plausible that ritual exchanges took place there, perhaps offerings, perhaps sacrifices to the Sidhe, possibly to repel or appease the forces of Winter.
3) The Night's Watch left the Nightfort during the reign of Jaehaerys, probably under pressure from the Iron Throne. The sharp decline in the number of black brothers (from ten thousand to less than one thousand) is another sign of a major reform.
4) We have Craster's offerings to the cold.
5) It's clear that Lord Mormont tolerates and even understands what Craster is doing. He brings him a remarkable axe as a present, treats him with deference and answers firmly any criticism of Craster. He tells Jon with insistence that the Night's Watch needs
men like Craster, perhaps in a sense that goes beyond the evident meaning that rangers sometimes take refuge at the keep.
6) It raises the question of whether Craster is continuing what the Night's Watch had been doing before the reform.
I am not sure why the Watch would make sacrifices to the Sidhe. But it makes sense that the Targaryens abolished the practice, just like they made the (not quite) whole north abolish the first night. The explanation comes full circle if the bastard children born out of the first night were given at the Black Gate. (So abolition of the first night went hand in hand with abolition of offerings of newborns at the gate.)
I wanted to make a completely different point when I started this post, but one thought led to another...
@Elaena: You are probably right. The weirwood I mentioned are probably younger than one thousand years. The weirwood of Raventree Hall might not count, since it has been dead for... one thousand years.
Edited by Bran Vras, 16 May 2012 - 08:54 AM.