The announcement comes few days after the death of Gilberto Benetton, a prominent member of the Italian family that controls Atlantia and a strong supporter of the acquisition.

It also follows the collapse in August of a motorway bridge operated by Atlantia's unit Autostrade per l'Italia, a disaster that exposed Atlantia to harsh criticism by the Italian government and risked jeopardising the deal.

The Italian infrastructure group said in a statement it had indirectly acquired 50 percent plus one share of Abertis.

Spanish builder ACS takes a stake of 30 percent in the Spanish motorway group, with ACS's German unit Hochtief holding 20 percent less one share in it.

Under the same deal, Atlantia has also bought 23.9 percent of Hochtief at a price of 143.04 euros per share, for a total consideration of 2.4 billion euros.

Shares in Atlantia were up more than 2.3 percent after the announcement, in line with a similar rise in Italy's bluechip index <.FTMIB>.

LONG-RUNNING BATTLE

Atlantia announced its intention to buy Abertis in May 2017 but a competing bid by ACS emerged some months later, locking the two companies in a bid war.

An agreement sealed last March between Italy's Benetton family and Real Madrid soccer club Chairman Florentino Perez, who heads ACS, created the basis for a joint bid.

The shares in Abertis will be held via investment vehicles Abertis HoldCo and Abertis Partecipaciones.

The 16.5 billion euros jointly invested in the transaction includes an equity injection of 6.9 billion euros in Abertis HoldCo.

The financing package for the deal includes a 3 billion euro amortising term loan, a 4.7 billion euro bridge-to-bond facility and a 2.2 billion bridge-to-disposal facility.

Lazard and JP Morgan advised ACS and Hochtief on the deal while Credit Suisse, Mediobanca and Santander worked for Atlantia.

(Reporting by Francesca Landini; Editing by Giulia Segreti and Edmund Blair)