The modern locution might be "like a horse in a pasture." A "common" was the common
ground set aside or simply taken over by a community for pasturage of the small flocks
and other animals belonging to its individual members. In the two generations previous
to the writing of Frankenstein commons had all but disappeared in the British Isles
as a result of their "enclosure" by landlords. The effect was enormously disruptive
of rural stability, as Oliver Goldsmith's well-known poem, The Deserted Village (1770),
recounts.