Serres in Greece and Petrich in Bulgaria are sister cities (since 2005), having cooperated in common E.U. projects, facing various common challenges such as: preservation of cultural heritage, protection of environment, promotion of resource efficiency, cross-border entrepreneurship, development of tourism. Initiatives in both cities are currently in progress aiming to utilise former military camps.
Serres and Petrich have a time distance of approximately 40 minutes by private car, including border controls, thus a visitor of the area staying in one of the cities may easily visit the other one, if there are good reasons for it.