Sister city
A sister city or a twin town relationship is a form of legal or social agreement between two geographically and politically distinct localities for the purpose of promoting cultural and commercial ties. While there are early examples of international links between municipalities akin to what are now known as sister cities dating back to the 9th century, the modern concept was first established and adopted worldwide during World War II. == Origins of the modern concept == Throughout history, many cities have participated in various cultural exchanges and similar activities that might resemble a sister-city or twin-city relationship, but the first officially documented case of such a relationship was a signed agreement between the leaders of the cities of Toledo, United States and Toledo, Spain in 1931.