feretrum

例句：

1. 1. The ancient city of Rome was built on a foundation of feretum, which is now known as the city's main source of iron.
   古罗马城建立在铁的基础上，现在被称为这座城市的主要铁源。
2. 2. The ancient Romans used feretum to make their weapons and armor.
   古罗马人使用铁来制作他们的武器和盔甲。
3. 3. The discovery of iron in the earth has revolutionized human history.
   在地壳中发现铁，已经彻底改变了人类历史。