Complex sentence: The city was built on a cliff on the south-coast of Sicily, surrounded by two rivers (the Hypsas and the Akragas), making it was easy to defend in times of war.
Split into simpler sentences: The city was built on a cliff on the south-coast of Sicily, surrounded by two rivers (the Hypsas and the Akragas). This position meant that the city was easy to defend in times of war.