Reconstructing their genomes confirms the historically attested genealogy of the two medieval emperors Otto I (the Great) and Heinrich II (Saint Henry)

Ancient whole-genome sequencing of the purported remains of medieval emperors Otto I and Heinrich II confirms their historically attested great-uncle/grandnephew relationship, thereby authenticating the remains and establishing them as valuable ground-truth resources for refining bio-archaeological dating methods and tracing elite European lineages.

The Gist

Imagine you have two very old, dusty family photo albums from a thousand years ago. One belongs to Otto the Great, a powerful king who ruled in the 900s, and the other to Henry II, his great-nephew who ruled in the 1000s.

For centuries, historians have looked at these albums (the bones in their graves) and said, "We think these are the real kings, and we think they are related just like the history books say." But there was a nagging doubt: Over 1,000 years, graves get opened, bones get mixed up, and skulls get moved around as holy relics. It was like trying to solve a puzzle where someone had swapped a few pieces with pieces from a different puzzle.

The Big Question: Are these bones actually who we think they are, and are they really related?

The DNA Detective Work

A team of scientists decided to act like genetic detectives. They didn't just look at the bones; they went inside them to read the "instruction manual" of life: DNA.

They took tiny samples from:

• Otto's remains in Magdeburg (specifically a tiny ear bone called the incus).
• Henry's remains in Bamberg (a skull and a thigh bone that had been kept as a holy relic).

Think of DNA as a giant, 3-billion-letter book that tells the story of your family. Even after 1,000 years, these books are torn and faded, but the scientists managed to piece them back together.

The "Aha!" Moment: The Family Reunion

Once they had the books, they compared them. Here is what they found, using some simple analogies:

1. The "Shared Pages" Test (IBD Segments)
Imagine you and your cousin both inherited a specific, unique story from your great-grandparents. You both have that same story written on pages 45 through 50 of your family books.

• The scientists found that Otto and Henry shared long stretches of identical "pages" in their DNA.
• The amount of shared DNA was exactly what you would expect if they were great-uncle and grandnephew. It was like finding the exact same family heirloom in both of their attics.

2. The "Father's Signature" (Y-Chromosome)
In this family, the "Father's Signature" is passed down from dad to son, unchanged, like a family crest on a coat of arms.

• Both Otto and Henry had the exact same Y-chromosome signature (called R1b-FTA63331).
• This is a very rare signature. Finding it in two men who lived 1,000 years ago and are supposed to be related is like finding two people in a crowd of a billion who both have the exact same, extremely rare tattoo on their wrist. It proves they came from the same male line.

3. The "Mom's Story" (Mitochondrial DNA)
While the "Father's Signature" was the same, the "Mom's Story" (passed from mother to child) was different.

• Otto had one version of this story, and Henry had a different one.
• This makes perfect sense! Otto's mother was different from Henry's mother. If they were the same person, the stories would be identical. The fact that they were different confirmed the scientists' math: they were related, but not the same person.

Why Does This Matter?

This isn't just about proving two old kings are who they say they are. It's like finding the "Gold Standard" or the "Control Group" for history.

• The "Ground Truth": Historians know exactly when Otto and Henry died (down to the day). Now, scientists can use their bones to test their tools. It's like having a stopwatch that you know is perfect, so you can use it to check if your other stopwatches are running slow or fast. This helps improve how we date other ancient bones.
• Solving Other Mysteries: Because we now know the "family code" of the Ottonian dynasty, if we find a random skeleton in a castle somewhere else in Europe, we can check its DNA against Otto and Henry's. If it matches, we might have just found a lost prince or a forgotten queen!

The Bottom Line

The scientists successfully opened the "time capsule" of the Ottonian dynasty. By reading the ancient DNA, they confirmed that yes, these are the real bones of Otto I and Henry II, and yes, they are exactly the great-uncle and grandnephew that history books have claimed for a thousand years.

It's a victory for history, proving that even after a millennium of dust, dirt, and moving bones, the truth written in our genes never lies.

Technical Summary

1. Problem Statement

The authenticity of the human remains attributed to Otto I ("the Great," r. 912–973) and Heinrich II ("Saint Henry," r. 1014–1024), the first and last emperors of the medieval Ottonian dynasty, has long been unproven.

• Historical Context: Historical records state these two were related as a great-uncle and grandnephew via the paternal line.
• Physical Challenges:
  • Otto I: His grave in Magdeburg Cathedral was last opened in 1844 with poor documentation; the tomb was reconstructed in the 13th century, and security was inadequate in the 19th century, raising risks of commingling or replacement.
  • Heinrich II: His remains were moved to a 16th-century tomb, but his skull and some bones were kept as relics outside the grave, and a femur was transported to Rome before being repatriated in 2024.
• Scientific Gap: There was a lack of genetic evidence to confirm if the skeletal remains in Magdeburg and Bamberg actually belonged to these specific historical figures or if they were mixed with other individuals over the last millennium.

2. Methodology

The study employed a comprehensive ancient DNA (aDNA) workflow to generate whole-genome data from the purported remains.

• Sampling:
  • Heinrich II: A petrous bone was sampled from Bamberg Cathedral.
  • Otto I: An incus bone (middle ear) was sampled from Magdeburg Cathedral.
• Wet Lab Procedures:
  • Extraction: Silica-based extraction optimized for short DNA fragments.
  • Library Prep: Single-stranded DNA library preparation with UDG half-treatment to reduce deamination errors while retaining damage patterns for authentication.
  • Sequencing: Performed on an Illumina NovaSeqX Plus platform.
• Bioinformatic Processing:
  • Pipeline: Used the nf-core/eager pipeline for standard aDNA processing (adapter trimming, mapping to hs37d5 reference, duplicate removal).
  • Quality Control: Filtered for base quality >30, mapping quality >25, and read length >30.
  • Contamination Estimation: Used hapCon (for nuclear DNA in males) and Schmutzi (for mitochondrial DNA). Both showed contamination levels well below 2%.
• Genetic Analysis:
  • IBD (Identity by Descent): Imputed diploid genotypes using GLIMPSE (1000 Genomes reference) and detected shared IBD segments using ancIBD.
  • Simulation: Compared observed IBD sharing against 1,000 simulated replicates of various relationship classes using Ped-sim to statistically validate the degree of relatedness.
  • Haplogrouping: Determined Y-chromosome and mitochondrial DNA (mtDNA) haplogroups by comparing variants against the FamilyTreeDNA Haplotree (Y-DNA) and Mitotree (mtDNA).

3. Key Results

A. Data Quality and Authentication

• Coverage: Achieved average genomic coverages of 0.996x (Heinrich II) and 0.576x (Otto I).
• Endogenous DNA: Heinrich II had 10.28% endogenous DNA; Otto I had 33.17%.
• Damage Patterns: Both libraries exhibited characteristic aDNA damage patterns (C→T deamination at fragment ends), confirming their antiquity.
• Sex Determination: Both individuals were confirmed genetically male.

B. Genetic Relatedness (The Core Finding)

• IBD Segments: The analysis identified multiple long shared IBD segments between the two genomes.
• Degree of Kinship: The empirical IBD sharing clustered perfectly with third-degree relatives connected via a full-sibling pair.
  • Genetic Definition: In genetics, a great-uncle/grandnephew relationship (where the link is through a full sibling) constitutes a third-degree relationship.
• Statistical Validation: The observed data was statistically indistinguishable from simulated third-degree relatives and distinct from other relationship classes (e.g., first or second degree).
• Conclusion: The genetic data confirms the historical record: Otto I is the great-uncle of Heinrich II.

C. Uniparental Haplogroups

• Y-Chromosome: Both individuals share the same rare Y-haplogroup: R1b-FTA63331.
  • This haplogroup is extremely rare in modern populations (<0.1% frequency in Germany/Netherlands).
  • The Time to Most Recent Common Ancestor (TMRCA) is estimated at 448 CE (95% CI: 105 BCE–876 CE), consistent with the Ottonian lineage.
  • This confirms an unbroken paternal line between the two emperors.
• Mitochondrial DNA:
  • Otto I: Haplogroup K1a4a1a2b.
  • Heinrich II: Haplogroup H7b2a.
  • The different mtDNA haplogroups are consistent with the genealogy (Otto I and Heinrich II's father were brothers, but their mothers were different).

4. Key Contributions

1. Definitive Authentication: The study provides the first genetic proof that the remains in Magdeburg and Bamberg are indeed those of Otto I and Heinrich II. It rules out the possibility that the graves contain unrelated individuals or that the "replacements" were coincidentally related.
2. Methodological Calibration ("Ground-Truth"): Because the exact birth and death dates of these emperors are historically documented, their remains serve as a "ground-truth" for:
   • Calibrating radiocarbon dating methods for Medieval elites (addressing reservoir effects).
   • Validating age-at-death estimation techniques in bio-archaeology.
3. Reference for Medieval Elite Networks: The high-quality genomes of the Ottonian dynasty provide a critical reference point for identifying and authenticating other Medieval elite burials across Europe, given the dynasty's extensive intermarriage networks with the Capetians, Salians, and Burgundians.

5. Significance

• Historical Resolution: This study resolves a millennium-old uncertainty regarding the identity of two pivotal European rulers, validating the historical genealogy against biological reality.
• Scientific Impact: It demonstrates the power of combining low-coverage whole-genome sequencing with advanced IBD detection tools (ancIBD) to solve historical mysteries even when sample preservation is imperfect.
• Future Applications: The data establishes a benchmark for future paleogenomic studies of the Middle Ages, offering a calibrated dataset to refine dating methods and trace the genetic history of European nobility.

Note on Publication Status: This text is a preprint posted on bioRxiv on March 20, 2026 (a future date relative to the current real-time, indicating this is a hypothetical or future-dated scenario in the prompt's context), and has not yet undergone peer review.