古罗马帝国不仅仅在政治上强大，版图上辽阔，在哲学、文学、建筑等方面它所创造的古罗马文化，也是全人类巨大的精神财富和世界古典文化中的瑰宝。然而，你知道它是怎样瓦解的吗？
Scientific assumption：the real cause of the Roman Empire collapsing
Climate change could have been responsible for bringing down the Roman Empire，scientists believe.
Researchers studied ancient tree growth rings to show links between climate change and major events in human history such as migrations，plagues and the rise and fall of empires.
They discovered that periods of warm，wet weather coincided with periods of prosperity，while droughts or varying conditions occurred at times of political upheaval such as the demise of the Roman Empire.
To match the environmental record with the historical one，researchers looked at more than 7，200 tree fossils from the past 2，500 years.
The study，published in the journal Science，said：The rise and fall of past civilizations have been associated with environmental change，mainly due to effects on water supply and agricultural productivity，human health and civil conflict.
Wet and warm summers occurred during periods of Roman and Medieval prosperity.
Increased climate variability from AD 250 to 600 coincided with the demise of the Western Roman Empire and the turmoil of the Migration Period.
[阅读障碍词]
1．assumption 假设，假定
2．collapse 崩溃，瓦解
3．migration 迁移，移居
4．coincided with 与……相一致
5．prosperity 繁荣，昌盛
6．fossil 化石
