Civilizational memory fails not because civilizations forget, but because the records they trust quietly shift beneath them. Clay tablets outlasted empires because they could not be edited after firing. Papyrus, parchment, and paper each introduced convenience at the cost of mutability. Digital storage accelerated that trade — instant replication, but also instant revision, silent corruption, and erasure without trace. The Bitcoin Timechain reverses the arc. It is the first substrate where a record, once anchored, cannot be retroactively altered by any party, for any reason, at any scale. That property is not a feature of money. It is the prerequisite for honest history. If a civilization cannot guarantee that what it witnessed yesterday remains unchanged today, it has no memory — only a story it keeps retelling. Immutability is not security theater. It is the floor under everything worth remembering.