Authors: Anil Kumar (@anilkumar827), Sattvik Kansal (@sattvikkansal)

Liquidity fragmentation has been the main objection to the Ethereum rollup-centric roadmap, amongst other problems such as weakest-link security and interoperability. This is mainly because sequencers, where users submit transactions, are isolated for each rollup. Since rollups have no visibility of each other, this means that transactions and liquidity on one rollup cannot easily interoperate with another. That’s why we have seen shared sequencer networks such as Astria and Espresso gain traction recently.

A shared sequencer enables rollups to launch quickly, provides atomic composability for cross-rollup transactions, and preserves decentralization. A shared sequencer network is a necessity for secure, decentralized, and scalable blockchains.

Shared sequencers also provide economies of scale; and allow for superior MEV searching by removing the uncertainty around latencies for multiple sequencers, which can allow for more efficient MEV searching.

Cross-rollup atomic transaction inclusion offered by existing shared sequencers gives weak interoperability used by optimistic rollups. Stronger guarantees are needed for cross-rollup transactions such as bridging, arbitrage, and liquidity trades. This can be achieved using atomic conditional transaction execution, which can be done by shared sequencers.

All shared sequencers being built today are going to run into another problem: they will need a sizable stake to be effective in delivering on the shared sequencer promise of atomic composability. We will need to bootstrap billions of dollars of economic stake to secure the network.

Rather than starting from scratch, what if we leverage existing validators from a PoS blockchain to act as a shared sequencer network? Introducing Rome Protocol, which turns Solana into a shared sequencer.

Why use Solana?

Why use SOL instead of restaked ETH? A shared sequencer can just use EigenLayer to leverage restaked ETH for security, right?

Using SOL provides several benefits that are otherwise either not possible or require investment, time, and testing to reach Solana's level of capability. We highlight a few of these benefits below by comparing three different approaches.

How will it work?

Rome Protocol will provide a shared sequencer network deployed on Solana as smart contracts.

Each rollup on the shared sequencer network will be represented by a Neon EVM deployment. By doing separate deployments of Neon EVM for each rollup, the state of the Neon EVM deployment will be identical to the state of the rollup. Since the states are identical, a transaction will revert on the rollup if and only if it reverts on the Neon EVM deployment.

The canonical fork of Solana is unlikely to miscalculate whether a transaction reverts since the economic stake of the Solana network ensures its correctness.

Rome Protocol’s transaction flow is outlined in the diagram below.

Rome Protocol’s high-level architecture is outlined in the diagram below.

Below we show a comparison of different shared sequencing solutions.

Atomic Composability

Transactions going through Rome Protocol's sequencer are secured by Solana L1 and confirmed on the Solana chain before submission to the base layer. Rome Protocol ensures the atomic composability of related transactions via our Atomic Composability Layer.

Bridging

For example, Rome Protocol would support bridges as a mint agent for burn transactions on target chains. It would enable bridges to submit corresponding mint transactions to target rollups via the Rome Sequencer and atomically include them in the same block as the burn transaction.

Arbitrage and Liquidity/DEX

Rome Protocol would also support arbitrage and liquidity/DEX transactions by enabling the creation of corresponding transactions and atomically including them in the same batch.

Bundling and MEV

Transactions and bundles that do not need atomic composability will be made available to searchers for fair MEV ordering and to create bundles. Both MEV-ordered and atomically composed transactions will be validated via Solana shared sequencer and made available to rollups for soft commits. The bundler will be deployed on select SVM/Solana nodes.

Data Availability

This batch is then submitted to the Layer 1 data availability layer by the shared sequencer.

Economic Scheme

Shared sequencers provide economies of scale as more rollups use the same sequencer. As it unlocks use cases across the rollup ecosystem, it would offer several fee-based services:

• Fair and efficient MEV auctions

• Bridge service to enable atomic bridge transactions

• Cross-rollup arbitrage and DEX transactions

• Atomic execution of transaction across rollups for liquidity (defragment liquidity)

Why Now?

Rollups have emerged as the clear winner in scaling Ethereum. This means we need to optimize the speed at which transactions can be processed, streamline the deployment of new rollups, and improve atomic interoperability between rollups.

As more rollups emerge, MEV searchers will incur greater cost in globally optimizing across all rollups with varying latencies. By leveraging the single Solana L1 as a sequencer for all rollups, MEV searchers can more efficiently capture arbitrage opportunities.

When cross-rollup bundles don't exist, MEV searchers incur the opportunity cost of not having atomic cross-rollup transactions as shown in the example above. Rome Protocol’s native support for arbitrage and bridging addresses this opportunity cost.

Using Solana as a shared sequencer solves the above problems across rollup stacks such as zkStack’s hyperchains. Native bridging addresses the need for trustless bridging. Using Solana for shared sequencing provides fast proof aggregation. This all can potentially unlock the power of the hyperbridge and proof aggregation across the fractal landscape of zkEVM, which is unique to zkSync.

What's next?

Solana at its heart is an execution layer, perfectly poised to solve the pressing problem of cross-rollup liquidity fragmentation for the ETH community. It has a strong ecosystem of valuable partners such as Neon EVM and Jito that enable building our shared sequencing tech. It can help layer aggregation and hyperchains on zkSync that are leading the way to scaling Ethereum.

I have quit my job at JP Morgan to go full force on this project. If you're interested in joining me, shoot me an email at anil[@]romeprotocol.com. I would love to get the community's thoughts and comments on this.

Thanks to Omar Yehia (@omarryehia1) of @zkSync, Neel Somani (@neelsalami) of @EclipseFND, Rahim Noorani (@RahimNoorani2) of @SatoriFinance, Josh Bowen (@Jskybowen) of @AstriaOrg, Nick White (@nickwh8te) of @CelestiaOrg, Carl Lin and Trent Nelson of @SolanaLabs, and Sydney Huang (@0xSydney) of @EclipseFND for editing this blog post.