williamwright wrote:

I built a similar wall about twenty years ago. Mine was made from stones
that could be lifted by a JCB, and smaller ones. The wall was 4 metres
high so I had to build an ad hoc scaffold. It was keeping back ground
five metres high, the top metre being sloped back at 30 deg to the
horizontal.
I put in a concrete foundation and used concrete as mortar. I put weep
holes along near the bottom, and low down behind the wall left a gap
that I filled with rubble to allow the water to find the weep holes.
I angled the wall back at about 10 deg to vertical, and used smaller and
smaller stones as I worked my way up.

All sounds good, today they'd probably say just use compacted MOT type 1
instead of a concrete base, put geotextile against the back face, and
use perforated drain pipe instead the rubble at the base ...