Crypto Gloss

Layer 0

Layer 0 (L0) describes a class of protocols that provide foundational infrastructure on which Layer 1 blockchains are built or connected. The terminology is less standardized than L1/L2/L3 and means different things depending on context, but broadly encompasses three types: (1) cross-chain communication networks (Cosmos, Polkadot) that let independently-built L1 blockchains interoperate; (2) data availability layers (Celestia) that provide a substrate L1s post data to; and (3) network protocols (peer-to-peer layers, consensus bootstrapping) that underlie all blockchains. The L0 framing emphasizes that not all blockchain infrastructure is itself a “chain” — some layers exist purely to serve other chains.

Layer 0 Definitions

The term is used in three distinct ways:

Definition 1: Cross-Chain Communication and Shared Security

Cosmos IBC Framework:

  • Cosmos Hub and the broader Cosmos SDK ecosystem allows developers to build independent L1 blockchains (called “app-chains” or “zones”) that communicate via IBC (Inter-Blockchain Communication protocol)
  • Cosmos Hub itself is positioned as L0 infrastructure — not running applications, but serving as a routing hub for cross-chain IBC transfers
  • Each zone is a sovereign L1 with its own validators and token
  • IBC provides trustless message passing between zones

Polkadot’s Relay Chain:

  • Polkadot is explicitly designed as an L0: the Relay Chain provides shared security and cross-chain messaging to “parachains” (L1-equivalent parallel chains)
  • Parachains lease security from Polkadot rather than maintaining their own validator set
  • Polkadot’s L0 model: one validator set secures many parachains simultaneously
  • This “pooled security” is a different L0 design from Cosmos (where each chain is fully sovereign)

Definition 2: Data Availability Layer

Celestia:

  • Provides only ordering and data availability — not a compute environment
  • L1 chains and rollups post their data to Celestia and use its DA guarantees
  • In this sense, Celestia is “beneath” execution L1s, making it L0 in the stack
  • More precisely called a “DA layer” but often described as L0 in marketing

Definition 3: Physical/Network Infrastructure

Some teams (notably LayerZero the cross-chain messaging protocol, which uses “L0” in its name) use L0 to mean the underlying network transport layer — the peer-to-peer communication and message passing beneath blockchain consensus. LayerZero (the protocol) uses trusted “relayers” to pass messages between chains and is conceptually “below” individual L1s.

Cosmos as L0

Cosmos Hub (ATOM):

  • Originally the IBC routing hub; Interchain Security expanded its role to providing validator security to appchains (“consumer chains”)
  • ATOM stakers validate not just the Hub but also secured consumer chains (like Neutron, Stride)

IBC (Inter-Blockchain Communication):

  • Open protocol for trustless token and data transfers between Cosmos-SDK chains
  • ~100+ chains connected via IBC
  • Does not require centralized bridges — uses light client state proofs

Cosmos SDK:

  • Open-source framework for building sovereign L1 appchains
  • Provides modules for: staking, governance, IBC, token issuance
  • dYdX v4, Injective, Osmosis, Celestia all built on Cosmos SDK

Polkadot as L0

Relay Chain:

  • Core security layer; validators here secure all parachains simultaneously
  • No smart contracts on the Relay Chain itself (pure security provision)

Parachains:

  • Lease “slots” via auction or crowdloan; secured by Relay Chain validators
  • Run their own execution environments (EVM, WASM, custom VM)
  • Pass messages to each other via XCM (Cross-Consensus Messaging)

Cross-Consensus Messaging (XCM):

  • Polkadot’s analogue to IBC; allows parachains to exchange assets and call functions on each other
  • More flexible than IBC (can carry arbitrary instructions, not just token transfers)

Notable parachains: Moonbeam (EVM on Polkadot), Astar, Acala (DeFi hub), HydraDX (DEX)

L0 vs. L1 vs. L2

Layer Role Examples
L0 Cross-chain messaging, shared security, or DA beneath L1s Cosmos Hub, Polkadot Relay Chain, Celestia, LayerZero
L1 Sovereign execution chain with own validators/consensus Ethereum, Bitcoin, Solana, Cosmos app-chains
L2 Scales L1 by offloading execution; posts proofs back to L1 Arbitrum, Base, Optimism, zkSync
L3 Scales L2 further; appchain built on an L2 Xai (game L3 on Arbitrum), Degen Chain (L3 on Base)

Modular Blockchain Overlap

L0 and modular blockchain concepts overlap significantly:

  • Celestia is simultaneously described as “L0” and as the “DA layer” in the modular stack
  • The common thread: infrastructure that serves other chains rather than end users directly
  • L0 framing emphasizes hierarchy; modular framing emphasizes specialization and composability

Related Terms

Sources

Kwon, J., & Buchman, E. (2019). Cosmos: A Network of Distributed Ledgers. Cosmos Whitepaper.

Wood, G. (2016). Polkadot: Vision for a Heterogeneous Multi-Chain Framework. Polkadot Whitepaper.

Al-Bassam, M., Sonnino, A., & Buterin, V. (2018). Fraud and Data Availability Proofs. arXiv:1809.09044.

Zamyatin, A., Al-Bassam, M., Zindros, D., Kokoris-Kogias, E., Moreno-Sanchez, P., Kiayias, A., & Knottenbelt, W. J. (2021). SoK: Communication Across Distributed Ledgers. Financial Cryptography.

Westerkamp, M., Victor, F., & Küpper, A. (2020). Tracing Manufacturing Processes Using Blockchain-Based Token Compositions. Proceedings on Privacy Enhancing Technologies.