151
Autonomous excavator constructs dry stone wall
(electrek.co)
This is a most excellent place for technology news and articles.
Oddly enough, Spock solves the problem (because of course he does, and it's a comic that has to be done in 30 panels or so) by discovering that the city construction materials can be chemically dissolved into goo. Thankfully not the sort that overtakes a planet.
... at least assuming there wasn't a sequel.