  With the emergence of Miner Extractable Value (MEV), block construction
markets on blockchains have evolved into a competitive arena. Following
Ethereum's transition from Proof of Work (PoW) to Proof of Stake (PoS), the
Proposer Builder Separation (PBS) mechanism has emerged as the dominant force
in the Ethereum block construction market.
  This paper presents an in-depth longitudinal study of the Ethereum block
construction market, spanning from the introduction of PoS and PBS in September
2022 to May 2023. We analyze the market shares of builders and relays, their
temporal changes, and the financial dynamics within the PBS system, including
payments among builders and block proposers -- commonly referred to as bribes.
We introduce an MEV-time law quantifying the expected MEV revenue wrt. the time
elapsed since the last proposed block. We provide empirical evidence that
moments of crisis (e.g. the FTX collapse, USDC stablecoin de-peg) coincide with
significant spikes in MEV payments compared to the baseline.
  Despite the intention of the PBS architecture to enhance decentralization by
separating actor roles, it remains unclear whether its design is optimal.
Implicit trust assumptions and conflicts of interest may benefit particular
parties and foster the need for vertical integration. MEV-Boost was explicitly
designed to foster decentralization, causing the side effect of enabling
risk-free sandwich extraction from unsuspecting users, potentially raising
concerns for regulators.
