In the mid 1970s, the qualifying time for men (you have to qualify to run in the Boston Marathon in another marathon) was 3 hours--the per-mile pace is slightly less that 7 minutes per mile....for a 26.2 mile race. Around 1980, the BAA, which organizes that race cut that to 2 hours 50 minutes, about 6 minutes and thirty seconds per mile.
Found this in my Boston Marathon book by Tom Derderian.