Welcome to the 30 Day Challenge for July, where we’ll be looking at the STEM fields: Science, Technology, Engineering, and Math. I originally conceived of the as the Science & Math Challenge so those two categories will get more attention, but we will touch on all of them.

Today we want to know about what you think is the best invention created prior to the 20th century. It’s an arbitrary but defensible cutoff between the pre-modern and modern eras so we’re gonna go with it. Best can be based on any criteria you like: biggest impact on humanity, biggest impact on everyday life, most fun, most buttons, whatever.

Bonus: What pre 20th century invention would you like to erase from the timeline?