# Canonical Bridges

Execution chains often include a canonical bridge to their settlement chain. The canonical bridge inherits security from the settlement chain in the rollup case. Up to this point, interoperability only appears to be resolved.

Vitalik mentioned that [multi-chain not cross-chain](https://old.reddit.com/r/ethereum/comments/rwojtk/ama_we_are_the_efs_research_team_pt_7_07_january/hrngyk8/), because bridging along Ethereum's hierarchy does not introduce additional trust assumptions, and other types of bridging should be avoided.

<figure><img src="/files/P4WM9X5RbnlOpF4yADP7" alt="" width="563"><figcaption></figcaption></figure>

Unfortunately, two dark clouds linger over this idea of a "perfect tree,” indicating that the multi-chain network's topology may be far more complex and irregular:

1. Ethereum will not be the only settlement layer. Bitcoin, Solana, and others will more or less play the settlement chain role.
2. People want to move their assets from one execution chain to another arbitrarily. Moving assets along Ethereum's hierarchy inevitably involves expensive L1 gas fees, multi-step interactions, and sometimes [unbearable multi-day delays](https://kelvinfichter.com/pages/thoughts/challenge-periods/). From this perspective, “[L2 Interoperability](https://ethresear.ch/t/defining-l2-interoperability-a-first-attempt/9978)” becomes essential, even for the Ethereum ecosystem itself.&#x20;

<figure><img src="/files/k6Wr5bZpWAlR0pa9S66t" alt="" width="563"><figcaption></figcaption></figure>

[One meaningful solution](https://notes.ethereum.org/@vbuterin/cross_layer_2_bridges) is to supplement the canonical bridge with liquidity providers who add a layer that mitigates risk and facilitates rapid transfers. This method is effective for tokens with sound liquidity. However, it falls short for less popular, long-tail tokens.


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