Spey rods and spey casting have been around for quite a long time. They are said to have been developed in the 1800's in Scotland on the River Spey. Spey casting uses an exceptionally long (typically 12-16') two-handed rod. Spey rods/casting were evidently developed to make long cast for covering a lot of water (common in salmon and steelhead fishing). Another reason for their design was the fact that many of the Scottish salmon rivers are lined with trees and brush making a traditional backcast very difficult. These much longer spey rods allow for much longer "roll" casts. Another interesting thing is the the "back cast" is never a part of the spey cast. Personally, I have never fished with a spey rod but I have "tinkered" with one on several occasions. To me, a spey cast from a distance looks like someone with a 12 foot fly swatter doing battle with a swarm of nasty hornets.
An Introduction to Spey Casting Techniques - video by Greys Fishing
Ian Gordon's Spey Casting Masterclass - Ian Gordon and InTheRiffle