[33] Contract balances

Contract assets stood at €150.2 million (2018: €119.3 million); most of this amount, €143.6 million (2018: €114.7 million), was attributable to project business contracts. Of the contract assets recognised as at 1 January 2019, €91.5 million was billed in 2019 (2018: €88.1 million). By contrast, contract assets rose by €178.7 million year on year (2018: €213.8 million) as a result of goods and services already provided that will be billed only once the contractually agreed project milestones have been reached.

Of the contract liabilities, €416.8 million was attributable to project business contracts with a net debit balance due to customers (2018: €498.7 million) and €88.1 million to prepayments received from customers (2018: €71.4 million). They relate to services that are still to be provided but for which prepayments from customers have been received. Contract liabilities are recognised as revenue as soon as the contractual goods and services have been provided. The revenue recognised in the reporting period that was included in the contract liability balance at the beginning of the period amounted to €468.7 million (2018: €292.6 million). Prepayments received from customers came to €549.6 million (2018: €558.3 million).