Madrid: Historians searching for the tomb of Spain’s greatest writer, Miguel de Cervantes, said on Monday they had found fragments of a coffin with his initials on it, under a convent where he may have been buried.

Four centuries after the writer of Don Quixote died, experts have been trying to locate his remains in the hope of establishing an official burial site that would attract tourists and literary pilgrims.

They began using ground-penetrating radar last April to explore the sub-soil of an old brick-walled convent in the heart of Madrid where the writer had asked to buried.

Researchers said on Monday they had found some bones and a crumbling casket after digging in the crypt. A piece of the coffin had the letters “M” and “C.” on it, spelled out in metal tacks, they said.

One of the forensic anthropologists in the research team urged caution, however, as the findings were preliminary.

“We can’t at all confirm that we have found Cervantes, we can’t guarantee this was Cervantes’ coffin either, but the reality is that we have found a very battered coffin which was falling apart, and some badly damaged bones in that corner of the crypt,” Francisco Etxeberria told a news conference.

At least seven graves have been identified under the convent, although only two have been opened so far.

Cervantes’ Don Quixote is recognized as one of the world’s greatest literary works and considered a precursor of the modern novel. He was buried in Madrid after his death in 1616, the same week in which William Shakespeare died.