The purpose of this article is to investigate the historical and cultural factors affecting semantic change of the following idiomatic expressions: Armarse la de San Quintin (with its synonyms, Armarla, Aarmarse la de Dios es Cristo, Armarse la marimorena, and Armarse la gorda), Estar en Babia and Estar en las Batuecas, No se gano Zamora en una hora (and Al buen callar llaman Sancho), Pasar el Rubicon, Quien fue a Sevilla perdio su silla, Salga el sol por Antequera, and Tomar las de Villadiego (with its synonym: Poner los pies en polvorosa). Without understanding ‘what happened in each place when the corresponding idiomatic expression was formed’, it is almost impossible to interpret the correct meaning of the expressions. In this article, I will argue that the diachronic consideration of place names and its synonyms is a key to understand the synchronic idiomatic meanings of the expressions.