Prepositions 

Prepositions are short words that are used together with nouns to indicate spatial, temporal or other kinds of relations. A preposition together with a noun is called a prepositional phrase. In Greek, prepositions require the noun to be in a specific case. For example, ἐν can only be followed by a noun in Dative case. Some prepositions can take nouns in different cases and would have different meaning depending on the case of the noun. For example, περι means "around" if used with accusative, but means "about" if used with genitive. 

Below, you can see a chart of spacial prepositions: