Railway sleepers are your friend.
We had a garden that sloped down about 7 feet in 30. Using sleepers to create terraces we soon made it manageable, but do make sure the sleepers are solid when you get them.
"Good" railway sleepers will ooze oil and diesel on a hot day, and are pretty much indestuctible. Just don't sit on them in your pale coloured summer dress. (this includes blokes too - you'll end up looking like a sooty shearwater)
"Bad" railway sleepers will rot at the ends and provide housing, nursery care, and primary education for wood louse, mice, rats, mushrooms.