Banco Santander is to absorb Spanish two banks, Banesto and Banif, closing 700 branches in the process.
Santander owns 90% of Banesto and will buy out minority shareholders with Santander shares at a 25% premium. It already owns all of Banif.
The three banks have 4664 branches in Spain between them. All the remaining branches will be branded as Santander.
Santander predicted that the merger would save 520 million euros (£422 million) per year in three years.
It also said the total number of bank branches in Spain is expected to fall to 30,000 by the end of 2015, down from 46,000 in 2008.