f the western frontier of Chih-li from
Shan-si. West of the Hwang-ho the Great Wall forms the northern
frontier of Shen-si, and west of Shen-si it keeps near the northern
frontier of Kan-suh, following for some distance in that province the
north bank of the Hwang-ho. It ends at Kiayu-kwan (98 deg. 14'E.) just
west of Su-chow. This part of the wall was built to protect the one
main artery leading from central Asia to China through Kan-suh and
Shen-si by the valley of the Wei-ho, tributary of the Hwang-ho. There
is a branch wall in Kan-suh running west and south to protect the
Tibetan frontier. The height of the wall is generally from 20 to 30
ft., and at intervals of some 200 yds. are towers about 40 ft. high.
Its base is from 15 to 25 ft. thick and its summit 12 ft. wide. The
wall is carried over valleys and mountains, and in places is over 4000
ft. above sea-level. Military posts are still maintained at the chief
gates or passes--at Shan-hai-kwan, the Kalgan pass, the Yenmun pass
(at the N. of Shan-si) and the Kaiyu pass in the extreme west, through
which runs the caravan route to Barkal in Turkestan. Colonel A.W.S.
Wingate, who in the opening years of the 20th century visited the
Great Wall at over twenty places widely apart and gathered many
descriptions of it in other places, states that its position is
wrongly shown "on the maps of the day" (1907) in a number of places;
while in others it had ceased to exist, "the only places where it
forms a substantial boundary being in the valley bottoms, on the
passes and where it crosses main routes. These remarks apply with
particular force to the branch running south-west from the Nan-k'ow
pass and forming the boundary of Chih-li and Shan-si provinces." In
Colonel Wingate's opinion the wall was originally built by degrees and
in sections, not of hewn stone, but of round boulders and earth, the
different sections being repaired as they fell into ruin. "Only in the
valley bottoms and on the passes was it composed of masonry or
brickwork. The Mings rebuilt of solid masonry all those sections
through which led a likely road for invading Tatars to follow, or
where it could be seen at a distance from the sky-line." The building
of the wall "was a sufficiently simple affair," not to be compared
with the task of building the pyramids of Egypt.[6]

_Climate._--The climate over so vast an area as China necessarily