Dairy cows at the Apostolic Palace of Castel Gandolfo, Italy The cows that graze the Apostolic Palace of Castel Gandolfo are used to make Pope-approved cheese, butter, yogurt and a durable, nontoxic paint used in restoration projects in Vatican City. (Photo: Franco Origlia/Getty Images)

Since his election, Pope Francis has established himself as an outspoken champion of environmental sustainability — a somewhat novel cause for the Bishop of Rome. In his landmark 2015 environmental encyclical Laudato Si ("Praise Be To You"), the Argentina-born pontiff urged all global citizens — not just the world’s 1.2 billion Catholics — to do their part and take utmost care of our "common home." Since then, he’s referred to climate change deniers as "perverse," classified environmental degradation as a sin and bestowed the commander-in-chief with some not-so-subtle recommended reading.

This all said, it only makes sense that Pope Francis’ strong environmental leanings are being incorporated into the massive maintenance and upkeep efforts of Vatican City's architectural significant buildings and art-stuffed grounds.

As reported by CNN, just one of the more old-fashioned-meets-future-friendly restoration methods deployed in Vatican City is the use of a traditional milk-based paint to touch up the exterior walls of Belvedere Palace. Built in the late-15th century by Pope Innocent VIII, this imposing palazzo is located just north of St. Peter’s Square and, among other things, currently houses treasured works of art as well as the Vatican’s one-and-only pharmacy. (It’s one of the busiest drugstores in the world, apparently; top sellers include designer fragrances and hemorrhoid remedies.)

While the walls of Belvedere Palace have been hand-patted with a durable mixture of cow’s milk, calcium hydroxide (caustic lime) and natural pigments as far back as 1484, the tradition is very much being kept alive thanks to Pope Francis, whose environmental encyclical is pulling double-duty as a sort of "guidebook for restoration work." (You can see more about the process in the video below.)

"We really tried to apply these non-invasive methods," Barbara Jatta, director of the Vatican Museums, tells CNN. "Non-invasive for the environment and for the people." (Appointed in December 2016 by Pope Francis, Jatta is the first female to serve as head of one of the world's most significant museums.)

No ordinary dairy

Since this is Pope Francis we’re dealing with, the milk in question isn’t just any commercially produced dairy product.

The unpasteurized milk comes straight from the sacred udders of cows raised on the grounds of the Apostolic Palace of Castel Gandolfo, the former official papal summer residence. Located about 16 miles southeast of Rome, the sprawling 17th century compound, which now operates as a museum, includes a 62-acre (mostly) organic farm that’s home to a variety of critters including free-range hens, donkeys, turkeys, rabbits and the aforementioned holy cows.

In 2015, Pope Francis made his namesake saint proud by opening the bucolic spread to visitors for the first time. (Previous pontiffs, including the swimming pool-installing Pope John Paul II, viewed Castel Gandolfo strictly as a private retreat and forbid public tours.) Much of the food produced at Pope Francis’ farm, including eggs, olive oil and a variety of cheeses, are sold on-site at a bustling farm shop that attracts tourists and locals alike.

"Everything in those orchards and fields is greener, healthier, tastier," local resident Gisella Bianchi told Newsweek in 2016. "The cattle, donkeys, ostriches, rabbits and hens are free to roam on a wide, lush estate without city pollution. The only bad thing is the smell of stables, which often sweeps through town."

Aerial view of Vatican City A view of the Vatican Museums, the Palace of Belvedere and the Sistine Chapel from above. (Photo: Wikimedia Commons)

Preserving the past, naturally

In addition to applying locally sourced papal milk to buildings, restoration experts at the Vatican Museums employ other nontoxic and ecological methods in safeguarding other sights within a minuscule, UNESCO-listed city-state that receives upwards of 5 million visitors per year.

Per CNN, the Vatican is at the "forefront of research" on the use of natural essential oils to protect the hundreds of pieces of priceless marble statuary spread throughout the Vatican’s scenic, highly trafficked gardens. While the al fresco locale of the art makes it all the more dramatic, it’s also highly vulnerable to the elements. Fungi and bacteria can also spread from the surrounding plants and soil and damage and erode the marble. Following several years of research into natural and safe (for restoration workers, for the environment and for the art itself) methods of preventing biological deterioration, the Vatican concluded that thyme and oregano oils, sourced from organic crops in Sicily, do a splendido job.

"The marble conservation laboratory at the Vatican is among the leading groups working on green and sustainable conservation solutions," Leslie Rainer of the Getty Conservation Institute tells the Wall Street Journal.

All and all, the Vatican Museums employs a full-time staff of over 100 to gussy up 500-year-old buildings with milk paint, sprinkle oregano oil on statues and carry out other cleaning and repair tasks that fall in line with Pope Francis’ vision of environmental stewardship. Most all jobs are performed in a traditional manner by hand; any sort of modern-day mechanical assistance is largely eschewed.

"We're not nostalgic for the past," the Vatican's chief architect, Vitale Zanchettin, tells CNN. "The point is that we think these solutions age better. They are tried and tested."

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

Vatican palace gets dairy-based makeover
Pope Francis' cows play a key role in a centuries-old restoration technique used on Vatican City's Belvedere Palace.