> For the complete documentation index, see [llms.txt](https://crosschain-alliance.gitbook.io/hashi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://crosschain-alliance.gitbook.io/hashi/core-concepts/block-header-relaying.md). # Block Header Relaying Block headers are at the heart of Hashi’s security model. Rather than just relying on arbitrary messages between chains, Hashi works by relaying entire block headers from one blockchain to another. This means that dApps can verify not only the content of a message but the actual state of the originating chain. * **Why Block Headers?**\ Block headers contain essential information about the state of a blockchain, including the hash of the previous block, timestamp, and the Merkle root of all transactions. By relaying these, Hashi ensures that cross-chain interactions are based on cryptographic proofs tied to actual blockchain states, making them much more secure than simple message relays. * **How Hashi Uses Block Headers**\ Multiple independent oracles relay these block headers, which are then aggregated and validated by Hashi. The result is a robust verification process where only confirmed, valid block headers are accepted, ensuring data integrity across chains. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://crosschain-alliance.gitbook.io/hashi/core-concepts/block-header-relaying.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.