> For the complete documentation index, see [llms.txt](https://docs.hemi.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.hemi.xyz/foundational-topics/the-architecture/blocks.md). # Blocks {% hint style="info" %} ## 📜 TL;DR: * **Blocks** in blockchain technology are packets of transactions and data, made secure through links to previous blocks. * Altering past blocks requires modifying all subsequent ones, a security feature. The Hemi Network enhances this by segmenting blocks into five-minute "**keystone**" intervals, with a security proof sent to the Bitcoin network every second interval. {% endhint %} *** ## 🌐 Overview * A block is a component of blockchain technology that contains transactions and their associated data. * Its security is enhanced because all subsequent blocks in the chain cryptographically reference it, reinforcing the integrity of the entire blockchain with each new block added. Tampering with an earlier block requires altering not only that block but also every block after it. *** ## 🟦 Hemi Blocks * In the Hemi Network, blocks are organized into **five-minute intervals known as keystones**. To inherit Bitcoin’s security, \*one Hemi Network state proof must be published to the Bitcoin network every two keystone intervals. \* * The first block of each interval **cryptographically references the previous two keystone blocks**, ensuring that the network cannot be reorganized without a 51-percent attack against Bitcoin itself, a scenario considered highly unlikely even for powerful entities like nation-states. --- # 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://docs.hemi.xyz/foundational-topics/the-architecture/blocks.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.