We conduct a public goods game in three small towns in the Indian state of Rajasthan. Due to historical military conquest, until 1947 these towns were on (barely) opposite sides of a colonial border separating British India from the Princely States. Our research design offers a treatment comparison between the towns of (British) Kekri and (Princely) Sarwar, and a control comparison between (Princely) Sarwar and (Princely) Shahpura. We find that participants in (British) Kekri are more co-operative (i.e., contribute more) in both home-town and mixed-town groups compared to those in (Princely) Sarwar. The latter differences are driven by individuals with family ties to the towns, and we find no differences in the control comparison. Our results highlight the enduring effects of colonial rule on social norms of co-operation.