A Thematic from Poland

Archaeology is the topic of this Polish issue, but what artifact is shown on the stamp? The item is a(n):

a) runic alphabet
b) settlement plan
c) warrior’s shield
d) ancient abacus

You can split the treasure with Indiana Jones if you answered (b).

From a 1966 set celebrating Polish prehistory, this stamp shows a settlement plan for the ancient town of Bikuspin, dating from 2500 BC.

Etched on stone, this remarkable artifact not only shows an orderly array of individual dwellings but a road into the community, a main gate, and a palisade designed to protect the town.