"An agreement has been reached with the player for two seasons," the Istanbul club said in a statement, adding he would be paid six million euros ($6.5m) per season.

The 34-year-old Italian international was welcomed on his arrival in Istanbul by hundreds of 'Black Eagles' fans.

The former Borussia Dortmund forward joined Lazio in 2016 from Sevilla and scored a club record total of 207 goals in 340 matches.

He holds the joint record for the most goals scored in a Serie A season with 36 in 2019-20.

But a checkered 2023-24 season during which he scored just seven league goals, saw the striker lose his indisputable starting status and suffer the brunt of the frustration of disgruntled Lazio fans.

He won three trophies during his time with Lazio -- the Italian Cup in 2019 and the Italian SuperCup twice.

An important player during Italy's European title success in 2021, the 57-times capped forward with 17 goals was not selected for Euro 2024.

Immobile's mission will be to revitalise the Besiktas attack: the 16-times Super Lig champions last won the title in 2021.

Last season they finished sixth, more than 40 points behind champions Galatasaray and second-placed Fenerbahce, its two great Istanbul rivals.