Slime Mold Has an Uncannily Accurate Sense of Where Rome Built Its Roads

The strange organisms are remarkably good at mapping the most efficient route from place to place—and that’s exactly what roads do

slime mold
The slime mold, physarum polycephalum Dr. Ken Wagner/Visuals Unlimited/Corbis

Bits of the Roman Empire's legendary roads seem to turn up everywhere, lying where a new subway line is meant to go, under Jerusalem neighborhoods or crumbling and nearly forgotten in the countryside. But if humans aren't always sure where Rome built its roads, another species—oozing, brainless slime mold—has an incredibly accurate sense of where the networks might have been.

This isn’t crazy. Despite their brainless state, slime molds—giant amoebae containing millions of nuclei—are curiously smart. As Joseph Stromberg explains for Smithsonian, "The slime mold, it turns out, is specifically evolved to do one thing very well: efficiently transport nutrients from one location to another." This has led researchers to use the creatures, for example, to design the most logical routes for the U.S. Interstate Highway System (if we were rebuilding it, that is).

Another research group has now used slime molds to map out the routes between ancient Roman cities in the Balkans. They simply placed food—oat flakes—on an agar map of the region, in the historical locations of 17 major Roman cities, reports Kelsey D. Atherton for Popular Science. She writes:

The mold was placed initially on the oat flake for Thessaloniki, a city in the northern Aegean region that was a major urban center at the time (and still the second-largest city in Greece today). The researchers ran the experiment 18 times, with the mold starting its spread from Thessaloniki for each run. The molds recreated with remarkable accuracy a network of roads similar to that used by the ancient Romans, even tracing out paths of relatively unknown and obscure roads like the West-Pontian road traveling northeast though the Balkans.

The researchers, whose aim was to put the slime mold through its paces and introduce an interdisciplinary tool to fellow archaeologists, published their work in the Journal of Archaeological Science: Reports.  They didn’t credit the slime mold as one of the authors. But then the slime mold probably doesn’t care about that as long as it can munch on oat flakes.