Definition
A blockchain bridge is a smart contract system that enables you to move assets from one blockchain to another. Because blockchains are isolated networks — Ethereum cannot natively read Polygon's state, and vice versa — bridges provide the coordination layer that makes cross-chain asset movement possible.
How Bridges Work
Most bridges use a lock-and-mint or burn-and-mint model:
-
Lock-and-mint: You deposit your token on the source chain into a bridge contract. The contract locks your token. A corresponding "wrapped" version is minted on the destination chain and sent to your address there.
-
Burn-and-mint: The source-chain token is burned (destroyed). The destination chain mints a canonical equivalent. Used by some native bridges (e.g., Circle's CCTP for USDC).
When you move back, the process reverses: the wrapped token is burned on the destination chain, and the original is unlocked on the source chain.
Types of Bridges
Native Bridges
Official bridges operated by the chain itself. For example:
- Polygon PoS Bridge (Ethereum → Polygon)
- Arbitrum Bridge (Ethereum → Arbitrum)
- Optimism Gateway (Ethereum → Optimism)
Native bridges are generally the most trusted but can have longer wait times (e.g., Optimism's 7-day withdrawal challenge period).
Third-Party Bridges
Aggregators and specialized bridges like Hop Protocol, Across, Stargate, and LI.FI. These often offer faster finality than native bridges and support more chain pairs.
Aggregated Bridges
Services like Socket and LI.FI route your transfer through the optimal bridge based on speed, cost, and liquidity. MovingWallet uses aggregated routing for bridge steps in migration plans.
Bridge Risks
Bridges are one of the most complex pieces of blockchain infrastructure and have been the target of high-profile exploits. Key risks include:
- Smart contract vulnerabilities in the bridge contracts themselves
- Liquidity risk — the bridge may not have enough of the destination token to complete the transfer
- Finality delays — some bridges (especially optimistic rollup withdrawals) have mandatory waiting periods
MovingWallet selects bridge routes based on security track record and liquidity, and simulates bridge transactions before submission.
Bridges in Wallet Migration
When a migration plan requires moving assets between chains, bridge steps are inserted automatically into the plan. Each bridge step includes:
- The bridge protocol to be used
- Expected wait time
- Estimated fees
- Simulation of the expected output amount
You sign the bridge deposit transaction from your source wallet. After the bridge completes, the assets appear in your destination address on the target chain.