The Urn of Life is what appears to be a terra-cotta urn with four red gems on the front in a distinctive cross shaped pattern, a design shared with the Genie's Lamp.
Before Series Edit
The Urn of Life was given to Empress Himiko by 'The Firebird' (Akai Tsubasa) at an unknown date, and at that time was said to hold beads of Akai's blood, which allowed Himiko to live for hundreds of years. 
In the past, Dark Eye's parents were in search of it for its ability to cure diseases and prolong life. 
Season 4 Edit
- The Empress Himiko in this urn's history is a reference to a real (or at the very least well-known in history/myth) Himiko. It's interesting to mention that the real world equivalent of Empress Himiko lived long after Akai has been sealed, so it's reasonable to assume that the timeline is sigificantly shifted backwards for her, and she lived up until the point she is stated to die due to the orbs contained within the Urn of Life in Kaitou Joker's setting.