Complex sentence: All these items are either directly imported from Minoan Crete or imitating Minoan models, a fact attesting to the intensive relations between Crete and the Peloponnese in this formative period of the Mycenaean civilization.
Split into simpler sentences: All these items are either directly imported from Minoan Crete or imitating Minoan models. These items demonstrate that there was extensive relations between Crete and the Peloponnese in this formative period of the Mycenaean civilization.