The influence of spatial concepts on the concept of time is a matter of fact as many expressions of temporal relations borrow directly from spatial language (dalla mattina alla sera vs. dall'ufficio all'universita) . These borrowings are not random but motivated by the fact that time is understood in terms of space. According to cognitive paradigm, metaphorical extensions preserve the source domain's mapping. The structures from both domains then are not only syntactically isomorphic but also semantically isomorphic. The article, in fact, deals with the problem of isomorphism in structures that relate to space and time. The conclusion is that the same prepositional units which are used in spatial contexts and in temporal ones have the same conceptual meaning based on the same image schemata (path schema, container schema) structuring both space and time. The linguistic data analysed in the paper confirm the above stated conclusion.