When you say 'rotted' - did they look something like this?
If so, that's called 'blossom end rot'. It usually indicates a lack of calcium in the soil, but it can also happen when it's very hot and dry, or if there is a lot of fluctuation from drought to rain during the growing season.
Not much you can do once you start seeing it, but mulching helps a lot (keeps the moisture level more constant). You can also add some lime in small amounts which will boost the calcium content.
I'm sure it's the intense heat that caused it this year.
I am a Nazi when it comes to keeping my sol levels straight, and this was the first year that I did mulch the garden. I had blossom end rot the first year I did them a while back, and learned all about it, but that's not what's happening this year.
Let me see if I can accurately describe this......when the tomatoes would form, they would get just under harvesting size, but they do it in a rapid time frame. However, once they get to that point, they don't grow anymore and they don't ripen.
On one plant in particular, I had a vine full of green tomatoes that were about full size and sat without ripening for 6-8 weeks. As you know, to call this abnormal would be an immense understatement. Then out of nowhere, the entire fruit would shrivel up like a giant raisin.
Out of all the things I've dealt with in the garden over the years, this is easily the most baffling. The thing that sucks, is they aren't even the green tomatoes I can fry up and eat, they are super dark green and rock hard, which is completely inedible.
My wife decided to pull some off and sit them in a paper bag to see if they would ripen, and put some in the window too. That was 3 weeks ago, and they are just as green and hard as they were when she brought them in.
Something about them is preventing them from ripening, and I'm at a complete loss. On the bright side, my cucumbers/zucchini/eggplant/broccoli are having record output far exceeding what I've been able to produce in the past. On the surface, that sound like maybe they are robbing the tomatoes, but that wouldn't explain why my neighbors tomatoes are doing it too.
I'm at the point now that I'm not even pissed about it, it's become more like trying to solve a murder