If you were near water, particularly moving water(stream, river, etc.) I'm gonna guess what you were seeing was one of two things.

1) A swarm of caddis flies, an aquatic insect that gathers in huge numbers along streams before ovipositing; that is, dropping eggs on the water.

2) It could also have been a swarm of mayflies beginning their final act of female ovipositing, and male fertilizing, both of which take place over water. Once accomplished, the adults die and drop to the water flat-winged. This is called a "spinner fall." Adult mayflies have no mouths, they don't eat, they live but about one full day. Hope this helps. Cheers!

I once attended a Pirates game, as the mayflies were swarming on the river. ICK! Nasty!

However, its a good sign that the river is returning to health.

oh! ok. are they (caddis or mayflies) large? these were kinda mosquito-looking...maybe a little bigger. they didn't seem to be falling. they were sort of going in an upward spiral. they were over water...right under the bridge is the river and the sewage treatment plant.