Which ancient library had half of it's structure burnt to the ground ?

Answer 1

Would it be this one:

"The 'Royal Library of Alexandria' in Alexandria, Egypt, was once the largest library in the world. It is generally thought to have been founded at the beginning of the 3rd century BC, during the reign of Ptolemy II of Egypt. It was likely created after his father had built what would become the first part of the Library complex, the temple of the Muses — the Museion, Greek Μουσείον (from which the modern English word museum is derived).
It has been reasonably established that the Library, or parts of the collection, were destroyed by fire on a number of occasions (library fires were common and replacement of handwritten manuscripts was very difficult, expensive and time-consuming). To this day the details of the destruction (or destructions) remain a lively source of controversy. The Bibliotheca Alexandrina was inaugurated in 2003 near the site of the old Library.
Ancient and modern sources identify four possible occasions for the destruction of the Library:
Caesar's conquest 48 BC;
The attack of Aurelian in the 3rd century;
The decree of Theophilus in 391;
The Muslim conquest in 642 or thereafter.
Each of these has been viewed with suspicion by other scholars as an effort to place the blame on particular actors. Moreover, each of these events is historically problematic. In the first case, there is clear evidence that the Library was not in fact destroyed at that time. The third episode has had some strong supporters, including Edward Gibbon, but still many dispute this.[7] The fourth episode was not documented by any contemporary source, although some maintain that the final destruction of the Library took place at this time.[8]"

Answer 2

That has been a fairly common occurrence throughout the ancient times. Put enough oil lamps and papyrus scrolls in the same building, and a major fire is only a matter of time.

The most famous of those fires, as other posters correctly noted, is the fire in the Alexandria library.

Answer 3

Library of Alexandria in Egypt

Answer 4

"It formed part of the research institute at Alexandria in Egypt that is known as the Museum, or Alexandrian Museum."

"A subsidiary "daughter library" was established about 235 BC by Ptolemy III in the Temple of Sarapis, the main museum and library being located in the palace precincts, in the district known as the Brucheium."

"The museum and library survived for many centuries but were destroyed in the civil war that occurred under the Roman emperor Aurelian in the late 3rd century AD; the "daughter library" was destroyed by Christians in AD 391."

Answer 5

Alexandria