June 25, 2015 6:23 AM EDT

1 The bot extrudes cords of molten steel in a pattern and waits for them to cool before moving ahead–like a train making its own tracks

2 Along the way, software continuously monitors for engineering errors and instructs the bot to correct course if necessary

3 When the 24-ft. (7 m) bridge is done (it’s expected to take two months), it will support foot traffic and feature intricate designs

This appears in the July 06, 2015 issue of TIME.

Contact us at letters@time.com.

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