Blue 2002,
If your Marathon's were a number of years old, they may have been the old style of tire which had a tendency to do just what your tire did. They, possibly, may have had just the polyester and steel belts in the tread. When those got hot, they would expand and get larger and then cool down and get smaller. Eventually, the tread area of the tire would just let go.
The new Marathon's are engineered with an additional belt of nylon on the outside of the polyester & steel belts. The nylon does not expand when it gets hot and has a tendency to limit the expansion of the polyester & steel belts. It acts like a girdle.
This, of course, doesn't mean that a new style of Marathon can't blow. Anything can happen. However, I don't hear of anywhere near the number of failures of the new tires as compared to the old style.
Last summer, I took an 8000+ mile trip, back east, and the summer before that, I took a 6000+ mile trip, plus many side trips around the desert southwest. All on the new style Towmasters (same tire as Marathon's), with no problems, at all. Two of my friends bought the Towmaster's and a third will this year. None of us have had a problem. My guess is the problems Marathon's were having is now fixed.
As a side note, one of my friends had the old style Marathon, watched his tire preasures religiously, had one blow on a trip back east, bought all new Marathon's (new style) but, kept the best looking old one for a spare. When he got back to AZ, the spare had blown, and it wasn't even on the ground. It was on the back bumper, spare tire mount.
Joe F. (Buffalo)