Life wasn’t terribly fair to Thomas Becket. In December 1170, after a lifetime of steadfast service as first chancellor to the king and then archbishop of Canterbury, the medieval Englishman was brutally beheaded by a troop of knights loyal to an embittered Henry II.

Nearly a millennium later, samples retrieved from a glacier in the Swiss Alps have revealed evidence of the squabble that hastened Becket’s demise: a plunge in the production of lead—a building material used in water pipes, stained glass and church roofs, among other architectural structures—borne out by the fallout between the church and the crown, which refused to support religious construction projects unless the archbishop accepted the king’s supremacy. After Becket’s murder, the ice reveals, lead use rose sharply again, testifying to Henry’s hasty scramble to redeem himself through the construction of a series of major monastic institutions.

These findings represent only a fraction of the discoveries recently described in the journal Antiquity. By recording traces of lead in its frozen flanks, the Alpine glacier featured in the study has unraveled a decades-long timeline of Britain’s mining industry that can be tied to major historical events immortalized in writing, reports Matt McGrath for BBC News.

Bored out of the Monte Rosa Massif on the Swiss-Italian border in 2013, the 200-foot-long ice core contained ancient bits of dust and pollution from the United Kingdom, ferried thousands of miles southeast by strong winds. Much like trees catalog their growth in annual rings, glaciers can store chemical snapshots of their environment through air bubbles trapped in accumulating ice. Modern researchers can then access the frozen archives via laser technology, according to a statement. This particular ice core contains roughly 2,000 years of history.

Homing in on medieval signatures of lead, the researchers found that 12th-century pollution was, at times, severe enough to rival levels seen during the latter half of the 19th century—after Britain had made the major switch to urbanization.

“Our notions of atmospheric pollution starting in the industrial revolution are wrong,” says lead author Christopher Loveluck of the University of Nottingham in the statement.

But medieval emissions also dramatically waxed and waned due to a bevy of sociopolitical factors, reports Harry Cockburn for the Independent. Mined for its versatility, lead found its way into coins, buildings, water pipes and even paint before scientists were able to quantify the extent of its toxicity. As such, the metal serves as a good proxy for times of prosperity and stability—periods when people had the luxury to grow their cities and spend their money. In line with this, the researchers found that lead production fell most dramatically during times of war and rebellion, as well as periods of transition between monarchs, usually immediately following a king’s death.

“The correlation between evidence of lead production in Britain in the ice core deposits and the tax paid on lead mines is astonishing,” says Loveluck in the statement. “We can see the deaths of King Henry II, Richard Lionheart and King John there in the ancient ice.”

Becket was no monarch. But his death, inadvertently triggered by Henry declaring, “Will no one rid me of this turbulent priest!”—an utterance of exasperation that his knights interpreted as license to kill—marked the culmination of a long and tense feud between Henry II and the church, one that temporarily stymied construction projects and, by extension, lead use.

Excommunicated in the wake of the murder, the king attempted to win back the pope’s favor by ramping those projects back up, Loveluck tells BBC News.

“And of course,” he adds, “massive amounts of lead were used for roofing of these major monastic complexes.”