Durante corresponds to during, while corresponds to mentre. The meaning of durante / during and mentre / while is the same, but durante / during is a preposition, mentre / while a conjunction. Durante / during stands in front of a noun, that's what prepositions normally do and while / mentre introduce a temporal clause.
Durante la sua assenza avevano, oltre che costrutito un edificio religioso, organizato molte feste.
During his absence they organized a lot of parties as well, besides that they constructed a religious building.
Durante la sua assenza, oltre ad avere costrutito un edificio religioso, avevano organizzato molte feste.
During his absence besides organizing a lot of parties they build a lot of religious buildings as well.