# Building the Transaction Merkle Tree

When two TXIDs are **concatenated** and **hashed**, the output depends on the **order** in which they were combined.

This order sensitivity means that the **Merkle Tree** can verify both:

* The **specific contents** of each transaction, and
* The **relative order** of transactions within a block.

As more transactions occur, the Merkle Tree grows — adding each new TXID as a **leaf node**.

After every update, the **Merkle Root** (a 32-byte hash) is recalculated, representing the **entire set of transactions** in the block.


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