What went wrong?

[Escarjoe]

I'm pretty new to 3D printing. I'm using an Ultimaker 2+ with PLA, a 4 mm nozzle, and the presets in Cura. I did switch it to the "fast" preset and I tried to print without supports. Everything seemed to be going fine when I left for the night, but in the morning the print was on the floor and there was a loose pile of extrusion on the bed of the printer. The nozzle is probably clogged now. This was a large size print, but I thought it was within the acceptable size range for the printer. The "arches" at the top were supposed to connect. I knew making these bridges might be a problem, but I kept the angles at 45 degrees thinking that would be gradual enough. Maybe the narrow pillars couldn't support the weight? Any ideas about what went wrong? Image attached. Thanks for your help.