Meridian walks in a straight line. This is the defining and most unnerving characteristic of a machine that has been doing nothing but walking north-south across the Iowa wasteland for as long as anyone has documented the Behemoths. Its path is precise to within two meters of an exact meridian line — not magnetic north, not grid north, but true geodetic north, as if it is calibrated to the planet's rotational axis. It walks south until it reaches a point near the Missouri border, then turns around and walks north to roughly the Minnesota line. Then it turns around again. The cycle takes approximately four months.

Meridian is bipedal — the only Behemoth that walks on two legs. It stands fifteen stories tall and has a roughly humanoid silhouette, which makes it the most psychologically disturbing of the Behemoths to encounter. Its 'head' is a featureless dome of sensor equipment that rotates slowly and continuously, scanning the horizon. Its 'arms' hang at its sides, swinging with its stride, and they end in complex manipulator clusters that have never been observed doing anything. The machine walks with a steady, mechanical rhythm that never varies — one step every 4.2 seconds, day and night, rain or shine, year after year.

The mystery of Meridian is its purpose. It doesn't harvest. It doesn't build. It doesn't manufacture. It doesn't collect. It just walks, measuring something with every step. Seismologists have noted that Meridian's footfalls generate precise, regular vibrations that penetrate deep into the earth — and that these vibrations are measurably different from random impacts. Some believe Meridian is conducting a geological survey. Others think it is a timing mechanism — a pendulum. A few suggest it is a message, written in footsteps on the skin of the earth, for a recipient that hasn't arrived yet.