Complex sentence: The cauldron measured 8.5 metres high, 8 metres across when flat on the ground and weighed 16 tonnes, significantly smaller and lighter than ones from previous events: the Beijing 2008 Summer Olympics cauldron weighed 300 tonnes.
Split into simpler sentences: The cauldron measured 8.5 metres high, 8 metres across when flat on the ground, and weighed 16 tonnes. It was significantly smaller and lighter than those of previous Games: the Beijing 2008 Summer Olympics cauldron weighed 300 tonnes.