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PARIS — A “forest” of wooden latticework inside Notre Dame Cathedral fueled the fire that consumed the iconic church.

The medieval roof structure “has been lost,” according to Monsignor Patrick Chauvet, the rector of the cathedral.

The cathedral’s wooden frame, which primarily consisted of oak, contains beams that date as far back as the first frame built for the cathedral. That frame featured trees cut down between 1160 and 1170, forming one of the oldest parts of the structure.

Most of the current frame dates from the year 1220, according to the church’s website. The modern frame is the second frame, and reflects adjustments made early in the cathedral’s construction process.

The prevailing Gothic style called for high vaulted ceilings. To accommodate this, the cathedral’s plans required tall, sturdy oaks from a nearby forest.

To kick off the project, workers cleared 21 hectares of oak. Each beam of the intricate wooden cross-work was drawn from a different tree: estimated at 13,000 trees in total. To reach the heights the carpenters needed to build the structure, those trees would likely have been 300 or 400 years old, meaning they would have sprouted out of the ground in the eighth or ninth centuries.

The beams formed one of the oldest structures in Paris.

The dimensions of the framework are soaring: 100 meters long and 10 meters high. At the nave of the church, the frame is 13 meters wide, and at the transept it’s 10 meters high, the church’s website says.

During the Middle Ages, the carpenters first built the frame on the ground to get the dimensions and structure right. Then workers would have disassembled the frame, hoisting it up with lifting gear to the ceiling, where it would have been reassembled. Once in place, the beams extended toward the heavens at steep 55-degree angles.

The wood frame structure supported a roof, made of lead, that weighed 210 tons. The lead frame had the advantage of being fire-resistant, according to the National Library of France. But the wood that supported that lead roof is what burned.

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What’s inside the cathedral of Notre Dame in Paris

Here’s an overview of some of the revered Gothic cathedral‘s most noteworthy features.

• The Great Organ has been replaced and updated several times throughout history. The position of titular organist, or head organist, carries great prestige in France and around the world.

• The Rose Windows are a trio of immense round windows over the cathedral’s three main portals.

• Numerous sculptures, statues and paintings inside the cathedral depict Biblical scenes and saints.

One series of 76 paintings, each nearly four meters tall, commemorates the New Testament’s Acts of the Apostles, including the crucifixion of St. Peter and the conversion of St. Paul. The works were completed between 1630 and 1707 by the members or associates of the Royal Academy of Painting and Sculpture.

Another painting is from a series by Jean Jouvenet depicting the life of the Virgin Mary. All six from the series used to be in the cathedral. They were moved to the Louvre in the 1860s, and only “The Visitation” was returned to Notre Dame.

• The twin bell towers, first constructed in the 13th century, were the tallest structures in Paris until the completion of the Eiffel Tower in the late 19th century.

• The cathedral’s main bell, Emanuelle, has marked significant moments in French history, such as the end of World War II, as well as holidays and special occasions.

• The cathedral’s treasury contains several artifacts sacred in Christianity, including what is believed to be the Crown of Thorns, a fragment of the True Cross and one of the Holy Nails.

• On the cathedral’s exterior, a menagerie of menacing gargoyles and chimères stand guard.

Paris Mayor Anne Hidalgo said earlier that most artworks and religious relics were removed from Notre Dame as firefighters worked to control the blaze.

France’s culture minister posted photos on social media of people loading art onto trucks.