A number of traits identify an urban society from a village. In the 1950s, V.G. Childe identified ten traits for an urban society, including permanent settlement in dense aggregations, centralization of surplus, monumental public buildings, social stratification, a ruling class, systems of recording and administration, exact and predictive sciences regulating the cycle of agriculture operation, conceptualized and sophisticated styles of art, long-distance trade and importing raw materials, and a social organization based upon residence rather than kinship. Although he identified these traits for ancient urban society, these also can be applied in modern times. The most important function of an urban society especially in southeast Iran is its intermediary function. This function can be seen both in ancient and modern times. The present paper aims to identify both urban societies in ancient and modern times, and to explain intermediary function of these societies, including Shahr-i-Sokhta during the third millennium BCE and Zahedan in modern time. In fact, this function may have caused the emergence and development of these urban societies during two different periods. It is also postulated that the decline of this function may have caused the collapse of both societies.