Immutable’s NFT Bridge Arch v1.0 to Connect L1 Ethereum With L2 StarkNet

To establish trustless connectivity for NFTs, Immutable has brought a new bridging protocol. Named Arch v1.0, the protocol will initially help native StarkNet NFTs bridge to the Layer-1 Ethereum seamlessly. The design of this ERC 721 protocol involves four contracts to ensure security, stability, and interoperability during the deposits and withdrawals.

Bridging protocols are commonly used when users want to send their fungible tokens across chains or layers. However, the same cannot be said for cross-chain NFTs transfers, mostly executed through the custom bridging protocols developed by the projects. The catch here is that these protocols greatly vary based on their security, stability, and other attributes, which may not be compatible with the network’s security guidelines.

Immutable has developed the new Arch NFT bridging protocol to trustlessly work with the tradeoffs of different rollups and chains. Arch will provide users with stability, interoperability, and an alternative to the restrictive NFT bridges currently being used.

The very design of Arch is accommodative of future iterations and improvements. But, as of yet, the bridge has only one use case: to securely connect the NFT collection of Ethereum L1 to StarkNet L2. The Arch NFT bridge is contract-agnostic, allowing developers to integrate their new or existing projects without facing compatibility issues.

Although the bridge is developed with the ERC721 standard, users can easily extend the bridge to other NFT standards like ERC1155. And what’s more, the bridge consists of a
four primary contracts, namely Bridge Registry, Escrow, L1 Bridge, and L2 Bridge, each with its execution.


The Bridge Registry will be the source of truth for the whole bridging operation through Arch. Initially, the Immutable team will oversee the token registrations until they know the security protocols. The team has deployed permissionless contracts on the Goerli testnet for beta testing.

The ERC721 Escrow is the lockbox for the tokens while they are being used in the L2 StarkNet. This contract’s functions are similar to the ‘wrapping’ operations on a fungible token bridge.

The ERC721 L1 and L2 Bridge contracts are responsible for the primary executions when people send or receive their tokens on Ethereum and StarkNet. They are also responsible for external functions, including ‘deposit’ and ‘withdrawal’, and help complete the bridging actions.

The Arch v1.0 has been launched as the first iteration of a much more ambitious project. The team is looking to extend the features and use-cases to a much wider range, including decentralization, automated contract deployment on StarkNet, L2 NFT withdrawals support, and multi-chain compatibility.

Immutable also welcomes developers and projects to test their compatibility and experiment with Arch on the Goerli testnet.