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 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 Shahpura. We find that participants from (British) Kekri are more co-operative in mixed-town groups. The differences are driven by individuals with family ties to the towns, highlighting the enduring effects of colonial rule on co-operation norms.