What is the origin of the idiom "since time immemorial" and when to use it?

The idiom "since time immemorial" originated in legal and historical contexts. It was used in English common law to describe a period that goes back so far that it happened before legal rights were established and refers to customs, practices, or rights that were believed to have existed since a time before written records or memory. It is often used when talking about the customs, traditions, rituals, and practices of ancient cultures or societies that have been passed down for a very long time. It emphasizes the idea that these cultural elements have been around since ancient times and have stood the test of time.