A modular blockchain separates the four core functions (execution, settlement, consensus, and data availability) into specialized layers rather than doing everything on one chain. Ethereum is becoming modular: L1 handles settlement/consensus/DA, rollups handle execution. Celestia is a dedicated DA layer. This specialization lets each layer be optimized independently, the way modern computers separate CPU, memory, and storage rather than putting everything on one chip.
What Is a Modular Blockchain (Structural Explainer)?
3 min read
The short version
Monolithic blockchains (old model) do everything on one chain: execute transactions, reach consensus, store data, and settle disputes. It is like one person doing every job in a restaurant. Modular blockchains split the work: one layer executes (rollups), one stores data (DA layer), one settles disputes (Ethereum L1). Each specialist does its job better than the one-person-does-everything approach.
How It Works
The four functions: (1) Execution: processing transactions and computing new state (which rollups handle off-chain for scalability). (2) Settlement: finalizing state transitions and resolving disputes (Ethereum L1 for rollups). (3) Consensus: agreeing on transaction ordering and block production (each layer has its own). (4) Data availability: ensuring raw transaction data is accessible for verification (L1 calldata, blobs, or external DA layers). The modular thesis: by splitting these concerns, you can optimize each independently. Rollups can experiment with different execution environments without compromising L1 security. DA layers can scale data throughput without needing to also process execution. The result is higher throughput, lower costs, and maintained security, at the cost of increased complexity and multiple trust assumptions. Key projects: Ethereum (evolving from monolithic to modular via rollup-centric roadmap). Celestia (dedicated DA layer). Avail (DA layer). EigenDA (restaking-based DA). Dymension (modular rollup framework). Fuel (modular execution layer).
A fully modular stack in practice
A new rollup wants maximum performance at low cost. They choose: Execution: their own rollup chain (custom VM optimized for gaming). Settlement: Ethereum L1 (submitting validity proofs for dispute resolution). Consensus: their own sequencer (initially centralized, decentralizing later). Data availability: Celestia (cheaper than Ethereum blobs, acceptable trust tradeoff for their use case). Result: transactions cost $0.001, settle in seconds, and can always fall back to Ethereum if anything goes wrong with the rollup itself. The tradeoff: users trust Celestia's validators for DA (smaller set than Ethereum), and trust the sequencer for liveness (not censorship resistance). For a gaming use case with small transaction values, this tradeoff is reasonable. For a $10B DeFi protocol, they might choose Ethereum DA for maximum security.
What People Get Wrong
Modular means less secure
It means security is distributed across layers with different properties. A well-designed modular stack can be as secure as a monolithic chain for the specific dimensions that matter. Ethereum L1 for settlement is the same security whether execution happens on L1 or a rollup. The question is which layers use which providers.
Ethereum is a monolithic blockchain
Ethereum is actively becoming modular. The rollup-centric roadmap explicitly moves execution to L2s while L1 focuses on settlement, consensus, and DA. EIP-4844 blobs made L1 a better DA layer. Ethereum is the settlement/DA layer in the modular thesis.
You need to understand modularity to use crypto
Users interact with rollups and apps without needing to know the backend architecture. Modularity is an infrastructure design choice that affects costs and security guarantees, but the user experience is just "use App X on Chain Y." It matters for evaluating security, not for daily use.
Keep Reading
Sources & Further Reading
- Celestia
The first dedicated modular data availability network
- Ethereum Rollup-Centric Roadmap
Vitalik post outlining Ethereum becoming the settlement/DA layer
Questions People Also Ask
- Is Celestia competing with Ethereum?
- Not directly. Celestia provides data availability (one modular component). Rollups can use Celestia for DA while still settling on Ethereum. They are complementary in a modular stack. The competition is between Celestia DA vs. Ethereum DA (blobs) as the DA provider for rollups, not between the chains themselves for end users.
- Does modular architecture fragment liquidity?
- Yes, this is the main UX challenge. Assets on Arbitrum, Optimism, Base, and zkSync are separate liquidity pools. Cross-rollup bridges, shared sequencing, and intent-based protocols (like Across, UniswapX) are working to make movement seamless, but fragmentation is a real current pain point.
- Will there be one dominant modular stack?
- Likely several. The Ethereum-centric stack (Ethereum for settlement + DA, various rollups for execution) is dominant today. Alternative settlement layers (Cosmos, Solana) have their own modular experiments. Competition between stacks will be decided by security, cost, developer tooling, and network effects over the next 3-5 years.