How to bridge from Layer 1 blockchains to Layer 2 blockchains

Bridging between Layer 1 and Layer 2 blockchains is one of the foundational user-facing operations in modern crypto. Most Ethereum mainnet users now have substantial holdings on at least one L2 (Arbitrum, Optimism, Base, ZkSync, Polygon zkEVM, or others). Moving assets between chains — the bridge transaction — is the operation that connects L1 holdings to L2 activity. The user-facing mechanics are worth internalizing as muscle memory because the patterns repeat across chains.

The canonical bridge flow. The user starts with assets on Ethereum L1 (most commonly ETH or USDC). They want to move those assets to an L2 (let's say Base) to use a DeFi protocol or hold for cheaper transaction costs. The user opens a bridge interface (the canonical bridge for Base is bridge.base.org, but third-party bridges like Across, Hop, or Stargate also work). They select the source chain (Ethereum), the destination chain (Base), the asset, and the amount. They approve the transaction on Ethereum. The bridge contract locks their assets on L1. After a delay (which varies by bridge mechanism), the corresponding assets become available on L2.

The mechanics under the hood vary based on bridge architecture. Canonical bridges (run by the L2 itself) typically lock assets on L1 and mint corresponding assets on L2. The trust model is the L2's own security guarantees. The withdrawal back to L1 typically requires a delay (7 days for optimistic rollups like Arbitrum and Optimism, much shorter for ZK rollups like ZkSync). Third-party bridges typically use a liquidity-pool model — they hold inventory on both chains and execute the swap faster, charging a small fee for the service. The trust model is the bridge protocol's own security.

The user-facing variables to understand:

Bridge time. Canonical bridges typically transfer L1-to-L2 in minutes but require 7 days for L2-to-L1 withdrawal (optimistic rollups). Third-party bridges typically execute in seconds to minutes in both directions.

Bridge cost. Includes the L1 gas to execute the deposit (variable based on network congestion), any bridge protocol fee (typically 0.05% to 0.3%), and the L2 gas for any post-bridge operations.

Bridge security. Canonical bridges inherit the L2's security model. Third-party bridges add their own security layer — bridge hacks have collectively destroyed billions of dollars across multiple incidents (Ronin $625M, Wormhole $325M, Nomad $190M).

Bridge slippage. For third-party bridges using liquidity pools, slippage can occur when bridging large amounts that exceed available pool depth.

The practical patterns:

For first-time bridges of significant amounts: use the canonical bridge. The trust model is the cleanest. The time delay on withdrawal is annoying but the security is best.

For routine bridges of moderate amounts: third-party bridges are typically faster, more convenient, and acceptable security risk for the bridge time savings.

For very large amounts: split across multiple bridges or stagger over time. Concentration in any single bridge transaction increases exposure to that bridge's specific risk.

The Block's primer covers the user-facing mechanics well. The patterns generalize across most L2 bridges, so internalize the basic flow once and you can navigate any new bridge interface with minimal friction.

One additional pattern worth knowing: as the L2 ecosystem matures, native asset issuance is becoming more common. USDC, for example, is now native on Base, Arbitrum, Optimism, and several other L2s — meaning Circle directly issues USDC on those chains rather than requiring users to bridge from L1. Native issuance eliminates the bridge step for many common use cases. Watch for this pattern; it's the right way for asset infrastructure to develop on L2s.