Why Blocks Are Linked Together

Most newcomers are comfortable with the basic idea of a transaction as a change in balances, and a block as a batch of those transactions grouped together. It is natural to picture blocks as separate files or folders that simply store what happened during a short period of time. What often feels abstract is the idea that all these blocks together form one long, shared history that really matters for how the system behaves. At first, it can seem like having a pile or list of blocks is enough, and that linking them together is just a technical detail. The key question is: if blocks already record transactions, why does the system bother to connect them into a chain at all, instead of just keeping many independent records? These intuitions are understandable, but they miss how much the system depends on one continuous, ordered history that all participants can check. Linking blocks is what turns a pile of transactions into a history that everyone can independently verify.

In a blockchain, each block does not just sit next to the others; it actually points back to the block that came right before it. Inside every new block there is a reference to the previous block, like writing the previous page number at the top of the current page. By doing this, the system makes inconsistencies visible and easy to detect, which later rules and consensus mechanisms can act on. It also gives the blocks a clear sequence: first block, second block, third block, and so on. The meaning of the later blocks assumes that the earlier ones are exactly what they claim to be. If someone tried to change a block in the past, the reference stored in the next block would no longer match what it is pointing to. That mismatch would then affect the block after that, and so on, so one change would ripple forward through every later link in the chain.

Because each block points to the one before it, new blocks are naturally added one after another, forming an ordered timeline. At any moment, there is a latest block at the tip of the chain, and that is the block that participants aim to extend. Honest participants who see the same chain will choose the same latest valid block as their starting point for the next block. This means they are all continuing the same story, instead of each writing their own separate version of events. Every later block depends on the earlier ones, because its reference assumes those earlier blocks have not changed. As more blocks are built on top of a particular block, that block’s position in history becomes more settled and harder to disturb without also redoing everything that follows it.

Imagine that blocks were just loose records in a folder, with no references to each other at all. This is why blockchains do not store transactions as independent records. Anyone could take those records, shuffle them into a different order, or quietly swap out one block for a slightly edited version. A computer receiving these blocks would see a collection of valid-looking records, but it would have no built-in way to tell which order they are meant to be in, or whether one of them has been replaced. Two different people could present two different sequences and both would look plausible on their own. Because nothing ties one block to the next, rewriting or reordering the past would leave very few traces. There would be no simple structural signal that one version of history is the original and another is an edited copy.

In a decentralized system, there is no single central server that everyone asks for the “official” history. Instead, many independent computers, often called nodes, keep their own copies of the chain and check it for themselves. Because blocks are linked, a node can start at the beginning and walk forward, verifying that each block correctly points to the one before it. If it encounters a block whose reference does not match the block it is supposed to follow, the node can see that something in that sequence is wrong. This simple structural check means that many different participants, spread around the world, can look at a proposed history and independently decide whether it is a consistent chain. When they all run the same kind of checks, they can compare histories consistently, and consensus rules can lead them to accept the same chain without needing a central owner to certify it. Linking alone does not create agreement, but it gives every node the same structure to verify before consensus rules decide which chain to accept.

Linking blocks together is powerful, but it does not mean that history is frozen the instant a new block appears. Very recent blocks can still be replaced by slightly different ones if there is a short period of disagreement about which block should be accepted. For the same reason, short competing versions of the chain, called forks, can temporarily exist near the tip before the system settles on one of them. The links make these situations visible and resolvable, but they do not prevent them from arising. Importantly, the chain structure does not depend on trusting a single party to maintain it correctly. Other ideas, such as how many blocks are built on top of a given block before it is treated as very stable, build on this structure and refine how confident participants feel about different parts of history.

A useful way to picture a blockchain is as a story written in a bound book. Each page in the book is like a block, and at the bottom of each page there is a note saying, “This page follows page X,” which is the link to the previous page. Because every page refers to the one before it, the book forms one continuous story from the first page to the last. If someone went back and changed an early page, many later pages would suddenly stop making sense or would contradict what they now say. In the same way, each block in a blockchain depends on the blocks that came before it. Changing one block in the past would disturb the meaning of all the blocks that follow, which is why altering history is not just a local edit but a change that affects the entire chain after that point.

Understanding that blocks are linked into a chain, rather than stored as separate records, is a core piece of how blockchains work. This idea explains why history matters, why order matters, and why changing the past is not a simple edit. The detailed tools that enforce these links, and the rules for choosing between competing chains, can be layered on top of this mental model later. For now, it is enough to see a blockchain as a bound story that many independent participants can read and check for themselves.