Mainchain

In practice, "mainchain" is the term used to distinguish a network's base blockchain from any dependent chain built to extend it, such as a sidechain or a rollup. Bitcoin and Ethereum are the two most cited mainchains: every other chain that connects to them, whether for scaling, privacy, or added smart-contract features, is judged by how closely its security and finality trace back to that base layer.

The link between a mainchain and a dependent chain is usually built with a two-way peg. A user locks native coins on the mainchain, and an equivalent amount of pegged tokens is minted on the connected chain; reversing the transfer burns the pegged tokens and unlocks the originals. Bitcoin-based sidechains illustrate the trade-offs well: Rootstock (RSK) uses merge-mining with Bitcoin's own miners for block consensus but relies on a federation of signers to manage the peg, while Blockstream's Liquid Network uses a federated multisig for both. In both cases, the sidechain runs its own consensus rules and cannot fall back on Bitcoin's mining power if its own security fails, so a compromised federation or validator set can put pegged funds at risk even though the mainchain itself stays untouched.

This is also the key distinction from a true Layer 2 rollup, which posts transaction data and validity proofs back to the mainchain and so inherits its security far more directly than a sidechain's federated peg does. Understanding which chain is the mainchain in a given system, and how a connected chain actually settles back to it, is essential for judging where the real security guarantees end and where a separate trust assumption begins.