Bridging Assets

City Chains leverage Arbitrum's native bridge infrastructure to enable secure asset transfers across layers. This canonical bridge provides the most secure path for moving assets between Ethereum, Locale Network (L2), and individual City Chains (L3).

Bridge Architecture

Multi-Layer Bridge Flow

Asset Bridging Layers

City Chain A (L3)

Local stablecoinLock tokens

Arbitrum Bridge Layer (L2)

Canonical bridgeState verification

City Chain B (L3)

Mint wrappedLocal stablecoin

Token Locking Model

Direction	Source	Destination	Mechanism
Deposit	L1	L2	Lock on L1 → Mint on L2
Deposit	L2	L3	Lock on L2 → Mint on L3
Withdraw	L3	L2	Burn on L3 → Unlock on L2
Withdraw	L2	L1	Burn on L2 → Unlock on L1

Supported Assets

Native Bridge Support

Asset Type	L1 → L2	L2 → L3	Notes
ETH	Native	Native	Gas token on all layers
USDC	Gateway	Gateway	Primary stablecoin
USDT	Gateway	Gateway	Tether stablecoin
ERC-20	Custom Gateway	Custom Gateway	Per-token configuration

Local Stablecoins

City Chains can mint local stablecoins backed by bridged assets:

Asset	Origin	Use Case
KCD (KC Dollar)	Kansas City	Local commerce, micropayments
USDC	Ethereum	Backing for local stablecoins
Bridged ETH	Ethereum	Gas, collateral

Gateway Contracts

L1GatewayRouter

The L1 Gateway Router manages deposits from Ethereum to Locale Network:

Function	Description
outboundTransfer	Initiates deposit to L2
getGateway	Returns gateway for specific token
setGateway	Registers new token gateway (admin)

L2GatewayRouter

The L2 Gateway Router handles the Locale Network side:

Function	Description
finalizeInboundTransfer	Completes deposit from L1
outboundTransfer	Initiates withdrawal to L1 or deposit to L3
getGateway	Returns gateway for specific token

L3GatewayRouter

Each City Chain has its own gateway router:

Function	Description
finalizeInboundTransfer	Completes deposit from L2
outboundTransfer	Initiates withdrawal to L2
mintLocal	Mints local stablecoin against bridged assets

Bridge Timelines

Deposit Times

Route	Typical Time	Notes
L1 → L2	~10-15 minutes	Includes L1 block confirmations
L2 → L3	~2-5 minutes	Faster L2 block times
L1 → L3	~15-20 minutes	Combined journey

Withdrawal Times

Route	Typical Time	Notes
L3 → L2	~7 days	Standard optimistic rollup window
L2 → L1	~7 days	Standard optimistic rollup window
L3 → L1	~14 days	Sequential withdrawal periods

Fast Withdrawals

For faster withdrawals, users can utilize:

Option	Time	Trade-off
Third-Party Bridges	Minutes	Liquidity fees
Fast Exit Providers	Hours	Service fees
Native Bridge	7+ days	No fees beyond gas

Security Model

Trust Assumptions

Layer	Security Source
L1 Bridge	Ethereum consensus
L2 Bridge	Arbitrum fraud proofs
L3 Bridge	Locale Network validation

Bridge Security Features

Feature	Protection
Fraud Proofs	Challenge invalid state transitions
Timelock	7-day window for challenges
Multisig Guardian	Emergency pause capability
Rate Limiting	Prevents large-scale exploits

Bridge Operations

Depositing to City Chain

1. Approve — Approve token spending on L1
2. Deposit to L2 — Call L1GatewayRouter.outboundTransfer
3. Wait for Confirmation — L2 processes the deposit
4. Deposit to L3 — Call L2GatewayRouter.outboundTransfer
5. Receive Tokens — Tokens appear on City Chain

Withdrawing from City Chain

1. Initiate Withdrawal — Call L3GatewayRouter.outboundTransfer
2. Wait for L3 → L2 — ~7 day challenge period
3. Claim on L2 — Execute withdrawal on Locale Network
4. Initiate L2 → L1 — Call L2GatewayRouter.outboundTransfer
5. Wait for L2 → L1 — ~7 day challenge period
6. Claim on L1 — Execute withdrawal on Ethereum

Integration with Local Currency

Stablecoin Minting

Bridged assets can back local stablecoins:

Local Stablecoin Backing

RESERVE BACKING

60%

USDC

Stable backing

30%

ETH

Growth asset

10%

Local RWA

Community assets

100%+ Collateralized

Verifiable on-chain reserves

Reserve Management

Metric	Transparency
Total Supply	On-chain, real-time
Backing Ratio	On-chain, auditable
Reserve Address	Public, verifiable
Mint/Burn Events	Indexed, queryable

Cross-City Transfers

Via Locale Network

For transfers between City Chains:

1. Withdraw to L2 — Bridge assets to Locale Network
2. Route — Locale Network coordinates transfer
3. Deposit to Target — Bridge to destination City Chain

Optimized Routing

Future implementations will enable:

• Direct L3 ↔ L3 — Atomic cross-city swaps
• Batch Processing — Reduced fees for bulk transfers
• Liquidity Pools — Instant swaps via shared liquidity

Learn More

• Cross-Chain Messaging — Message passing between chains
• City to City — Inter-city coordination
• Local Currency — Stablecoin economics