Blockchain & Cryptocurrency Glossary

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Sequencer Bridge

1 min read
Pronunciation
[see-kwen-ser brij]
Analogy
Think of a sequencer bridge as a mail sorter who collects letters, organizes them into bundles, and then ships the bundles to another city in one trip.
Definition
A cross-chain bridge that leverages a Layer 2 sequencer to batch, order, and forward transactions or state commitments to a destination chain.
Key Points Intro
Sequencer bridges connect Layer 2 ordering services with other blockchains for interoperable transactions.
Key Points

Batching & ordering: sequencer groups transactions into batches

Proof relay: posts state roots or Merkle proofs on the destination chain

Gas efficiency: reduces per-transaction costs by aggregating data

Trust model: relies on sequencer honesty and finalized batches

Example
Arbitrum’s sequencer batches L2 transactions and submits the resulting state root to Ethereum, enabling withdrawals and cross-chain interactions.
Technical Deep Dive
The sequencer node receives transactions, constructs a Merkle tree of L2 state, and signs a batch header. A relayer submits a transaction to the L1 bridge contract containing the batch root and calldata. The L1 contract verifies the batch via rollup or optimistic-rollup protocol rules and updates the canonical state. Challenge or fraud-proof windows may apply before finalization.
Security Warning
If the sequencer censors or withholds batches, users may face delayed withdrawals or stalled operations.
Caveat
Trust assumptions in the sequencer can pose centralization and censorship risks if not mitigated by fraud proofs or fallback mechanisms.
Related Terms
Rollup Bridge
Fraud Proof
Relayer Network

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