A young woman is offered as a sacrifice to save her people before being rescued by divine intervention. Then a war is fought. Years pass, and, now living some 2,000 miles away, the same woman receives an agonizing order to perform a sacrifice herself, another bloody gift to the gods.

That is a summary of two operas, both by Christoph Willibald Gluck: “Iphigénie en Aulide” and “Iphigénie en Tauride.” They were written five years apart and were never intended to be performed together. Each is a full-length score of about two hours, and while they share a protagonist, the vocal range for the character isn’t quite the same in both.

But their plots — which tell the story of Greek myth’s Iphigenia, first in Aulis as a would-be victim, then in Tauris as a would-be murderer — flow together with uncanny ease. And on Wednesday, the Aix-en-Provence Festival in France opened a production that pairs the works in a marathon double bill, directed by Dmitri Tcherniakov as a brooding reflection on the numbness of endless conflict.

Tcherniakov sets the two operas in a stage-filling, prisonlike skeleton of a house, with “Aulide” as the last gasp of a frivolous prewar elite. His “Tauride” depicts the somber aftermath of years of brutal battles, and the physical and emotional toll — the paranoia, the twisted fantasies — on those who remain.

Today, Gluck suffers a little from a reputation for formality, even stodginess. But with the period instrument ensemble Le Concert d’Astrée conducted gracefully yet energetically by Emmanuelle Haïm, the Aix double bill was a reminder of the vibrancy of his vision, a majestic yet vigorous directness.

This rare juxtaposition offers an immersion in Gluck’s revolutionary innovations — what became known as his reform of opera, paving the way for Wagner and modernity. By the middle of the 18th century, bloated extravagance was the mainstream of Italian opera, dominated by singers burbling mindless coloratura in an endless parade of arias that barely held together as narrative.

Gluck wrote in 1769 that these abuses had “turned the most sumptuous and beautiful of all spectacles into the most ridiculous and tedious.” To counter this, his aim was “to restrict music to its true function of helping poetry to be expressive and to represent the situations of the plot” — to seek “a beautiful simplicity.”

While this paring-down was forward thinking, it was also backward looking: a revival of the focus on the words in the first Italian operas of the early 1600s and the austere French tragédies lyriques later that century.

Gluck nods to those origins. But he goes further in eight works written in the 1760s and ’70s, when he was already decades into his career, and had written nearly 30 more conventional operas. These reform pieces helped introduce to the art form a new symphonic intensity and a pace that moves at something closer to spoken drama. (It can be hard to imagine today, but his operas were sometimes criticized for being too short.) Working with creative librettos, his music broke free of strictly regimented forms, instead responding flexibly to the rhythms of the story. He says as much as he needs to, and no more.

So, in “Iphigénie en Aulide” (1774), a father’s despair at the gods’ demand that he kill his daughter isn’t the occasion for a grand aria that stops the action, but rather a brief, tender outpouring that barely breaks it. “Iphigénie en Tauride” (1779) replaces the traditional stand-alone overture with a prelude that, in just two and a half minutes, depicts a calm sea erupting in storm, then melts — with no break for applause — into Iphigenia’s passionate prayer for the tempest to end.

This deference to the needs of the drama, the steady ratcheting up of tension through long scenes of continuous music that prefigure Wagner’s epic spans, is the key feature of Gluck’s reform. Few figures were more important in creating opera as we know it.

Gluck was born in 1714 in a small village in what’s now northern Bavaria, Germany, into a family of foresters and gamekeepers. He was no musical prodigy, but he developed his budding talent, and came of age amid the vogue for Italian operas driven by virtuoso singers, featuring librettos produced without any collaboration with the composers who set them. Though Gluck diligently produced many works in this vein, from the beginning he had little taste for coloratura fireworks; from a reform perspective, he didn’t have too many bad habits to break.

He was as much a vessel as an originator of the great change. “There were many people working on naturalizing the prevailing styles, and sort of domesticating them,” Stephen Wadsworth, who directed “Iphigénie en Tauride” at the Metropolitan Opera in 2007, said in an interview. Other opera composers, writers and impresarios around the same time were seeking greater simplicity, less complicated melodies, the merging of arias into the surrounding recitatives (sung dialogues), a more realistic acting style and less subservience to singers.

Gluck’s “Orfeo ed Euridice” (1762) was the culmination of these efforts, ushering in his trademark style. His librettist, Ranieri de Calzabigi, pressed him toward an organic union of words and music; the title role was sung by the castrato Gaetano Guadagni, who had worked with the English actor David Garrick, a pioneer of onstage naturalism.

“Alceste” premiered in 1767, and when the score was published two years later, Gluck’s preface set out his artistic credo, calling for an end to steady marches of da capo arias in favor of an unfurling drama, with fluidity through arias, recitatives and dance sequences, and a chorus that took a more vital part in the action. Supple and clear declamation dominated the scores: “Always as simple and natural as possible,” Gluck wrote.

“Iphigénie en Aulide,” his first opera written for Paris, was rehearsed for six months. (Simplicity is enormously complicated to achieve.) Controversy broke out over Gluck’s experiment, enough that Leopold Mozart warned his 22-year-old son, the already well-known Wolfgang Amadeus, against alienating any of the cultural elite by taking sides.

But Mozart made his choice clear: His masterly “Idomeneo” (1781) would quote Gluck in tribute. He was among the first composers to absorb Gluckian lessons — and was followed by pathbreaking giants like Cherubini, Beethoven, Spontini, Berlioz, Meyerbeer and Wagner.

“Iphigénie en Aulide” was enough of a success to inspire “Iphigénie en Tauride,” a kind of sequel — and also a maturation. There are more aria-like passages in the second opera, but their placement is more unexpected, and more responsive to the drama. At Aix, Haïm’s muscular conducting brought their styles closer together, playing down the nostalgic courtliness in “Aulide” that can make it a less fiery, elemental drama than “Tauride.”

In Tcherniakov’s concept, Iphigenia is from the start a passive figure, almost sleepwalking through a perfunctory marriage proposal from Achilles, then the terrifying prospect that her father, Agamemnon, will sacrifice her to ensure favorable winds to sail the Greeks to war in Troy.

Some 20 years later, she is serving as a kind of nurse or matron, perhaps in a prisoners’ camp, haunted by the ghosts of the dead she left behind, merely existing as history presses on around and past her. Her voice stern and hauntingly blank, the soprano Corinne Winters achieved a remarkable stunned stillness through a double bill that takes her from the light soprano territory of “Aulide” to the deeper mezzo-soprano range of “Tauride.”

The bitterly melancholy production reflected Gluck’s sobriety — and the molten feelings churning underneath. He didn’t directly train students who carried his mantle; even his own adoption of his reforms was inconsistent. But his ideas ended up charting the course of the art form’s future: his preferences about arias and choruses, yes, but far more important, his larger notion that opera must be, first and foremost, drama.