cross-chain bridge

Each blockchain is an island with its own ledger, its own rules, and no awareness of any other chain. A token on Ethereum cannot natively appear on Solana, because Solana's validators have never seen Ethereum's state and have no reason to trust a claim about it. A cross-chain bridge is the ferry service between these islands: a system that lets value and information move from a source chain to a destination chain, even though neither chain can directly read the other.

Almost every bridge is built from two halves: a way to observe that something happened on the source chain, and a way to act on the destination chain in response. The hard part is the observing. A contract on the destination cannot run Ethereum to check a deposit, so something must attest 'this deposit really occurred and is final'. Who provides that attestation defines the bridge's entire security model. At one extreme an external committee signs off (a trusted bridge); at the other the destination chain verifies the source chain's own consensus proofs (a light-client or validity-proof bridge). Most production bridges sit in between, with an external validator set, optimistic challenge windows, or economic bonds.

Mechanically, the asset transfer usually takes one of three forms. Lock-and-mint locks the original on the source and mints a wrapped IOU on the destination. Burn-and-mint destroys a native token on one side and re-issues it on the other so total supply is conserved. Liquidity-network bridges keep pre-funded pools on both sides and simply pay out locally, never moving the underlying. Beyond assets, general bridges relay arbitrary messages, letting a contract on one chain call a contract on another.

Bridges are the single most attacked surface in the entire industry: well over two billion dollars has been stolen from them. The reason is structural. A bridge concentrates the locked collateral of an entire chain behind whatever its weakest verification assumption is, so a flaw in a few signing keys or one proof check can drain everything. Treat the phrase 'bridged asset' as a reminder that you now also trust the bridge, not just the two chains.