When 4,000 mummified bodies were discovered in the crypt of this sleepy Spanish town a few weeks ago, researchers turned to their history books. What has tentatively emerged is a story involving the implacable Inquisition and a curious 16th century sect of Illuminati who indulged in baccanalian revelries.

The bodies were found at the base of the church tower in the village of Llerena, in the region known as Extremadura, in the west of Spain. The tower dates back to the 17th century and was built over the minaret of a mosque. Its present rickety state led to a plan to rebuild it and, in consequence, to a discovery of major historical and anthropological interest.

Hundreds of bodies are propped against each other in a dark, damp, walled-in dungeon. Most are unrecognizable, but a good meny are obviously men, women and children of different ages.

Llerena may well be a sleepy village now of little more than 5,000 inhabitants dedicated to barely subsistence farming. But it has all the traces of past grandeur, not least the church of our Lady of the Granada, with its whitewashed facade and its sandstone clock tower where the bodies were found.

In the 16th century it was a booming town of more than 15,000 people. Llerena's religious and civil jurisdiction then extended to the provincial capital of Leon, 400 miles to the north, and on its southern limits it reached Seville, more than 150 miles away, then the center of trade with the new world.

Llerena was a local headquarters of the medieval military-monastic order of the Knight of Santiago and it was a seat of the feared Inquisition, one of the 14 high tribunals fo the Holy Office installed in Spain between 1480 and 1637 to interrogate, torture and put to the stake all deviants from Catholic orthodoxy.

At this point, enter on to the stage of history the Illuminati. This particular Spanish sect was not dissimilar to other fanatical religious sects that fanned out across Europe before, during and after the Reformation. Historians have traced the Llerena Illuminati back to a religious movement founded in the city of Toledo in 1525.

This sect developed from an original mysticism, which owed much to the humanist Erasmus and his repudiation of the pomp, ostentation and corruption of the official church, into free-for-all sexual orgies.

The term Illuminati - people who profess to have special intellectual or spiritual enlightment - historically has been applied to several sects. The word means "illuminated ones" in Latin.

According to the Spanish religious historian Marceline Menedez Pelayo, "once the Illuminati achieved extasis, he became free from sin and all action thereafter was licit." According to the historian, Llerena became a "focal point of immortality and heresy."

Llerena was at this stage, along with the whole Extremadura region, entering into its period of decline. Extremadura, never a rich area due to its scarcely arable land, was the home of the conquistadors. As Hernan Cortes, Pizarro, and company left for the Indies to conquer Aztecs and Incas, the area was drained of manpower and the inflation caused by the returning riches did the rest. An inexorable slump was under way.

The scene was therefore set for the Illuminati to take roots among the dispossesed and for the Inquisition, empowered as it was with the sacred mission of stamping out unorthodoxy by fair means or foul, to smash them without pity.

That is at least the tentative explanation of the first researchers who have examined the Llerena find. The parish priest of the church, however, scoffs at such conclusions.

According to the Rev. Manuel Marin, "the only logical explanation is that there was a cemetery near the church and that the bodies were disinterred and placed in the crypt for lack of space. This is a simple ossuary, and nothing more."

Refuting the "simple ossuary" theory, two Spanish journalists investigating the find argued that the area where the bodies lie bore signs of a coverup operation.

The church of Our Lady of the Granada, built as it was over a mosque, was reformed, restructured and extended over the years. It is full of hidden altars, secret passages and staircases, false walls and double ceilings.

According to the journalists, the entrance to the site of the bodies was concealed by a large religious painting which had hung there for more than 200 years but was clearly painted for another area of the church. The site of the bodies lies between the present outer wall of the tower and and earlier wall built for the original minaret.

The small area involved appears to discount the theory that thousands of Illuminati, or others who fell foul of the law, were walled in and left to die. It is more probable that they were put to death, or died, elsewhere and then the bodies were transferred.

Whether the 4,000 or so died a natural death - perhaps in a plague as the parish priest would have it - or a violent one may be open to doubt. But the municipal records, already investigated, show no record of a sudden mass death sometime in the middle of the 17th century, which is when the mummies apparently date from.

The Inquisition records are all stored in the National Historical Archives in a castle in the town of Simancas, central Spain. When the rolls recording Lleren'as autos-da-fe as the Inquisition's trials and executions were known, are properly investigated some light may be thrown on a possible holocaust 330 years ago. CAPTION: Map, no caption, The Washington Post