Lydiard is the Godfather of running. He advocates at least 3 months of aerobic running. The longer the better. It's not all about easy running though. He talks about the "best aerobic state".
It's generally considered that he talked about 3 speeds in the base (conditioning) phase. Easy, steady and threshold, although he didn't necessarily use these terms.
Lydiard was before monitors etc, but in todays terms they equate to.....Easy about 70%WHR (working heart rate), Steady about 75%-80% WHR, and threshold about 85% WHR.
He always talked about your "best aerobic state" and believed in running to how you feel on that given day. It's all about raising your aerobic threshold. Something the African youngsters do without thinking, while they're running to school and back.