[34] Contract balances

Contract assets stood at €528.8 million (December 31, 2021: €519.1 million); most of this amount, €508.0 million (December 31, 2021: €504.2 million), was attributable to goods and services provided in the project business that have not yet been billed.

Of the contract liabilities, €640.3 million was attributable to project business contracts with a net debit balance due to customers (December 31, 2021: €675.0 million) and €185.8 million to prepayments received from customers (December 31, 2021: €179.8 million). The revenue recognized in the reporting period that was included in the contract liability balance at the beginning of the period amounted to €814.7 million (2021: €518.8 million).