Project notes
How the timeline was made
This is an editorial map of institutions, crowns and selected rulers. It is not a claim that every state had a clean birthday, that a dynasty was a single political actor, or that Europe can be reduced to forty-eight lines.
What is in scope
The timeline begins in 27 BCE, the conventional start of the Roman Principate, and ends in 2026. It includes sovereign monarchies that had a large effect on European political history, predecessor realms needed to explain later states, and all twelve sovereign European states that still have a monarch as head of state.
The dataset has two editorial tiers. Tier 1 contains the main continental story: Rome and Byzantium, Francia, France, the Holy Roman Empire, Britain, the Iberian crowns, the Nordic kingdoms, Poland-Lithuania, Kyivan Rus’, Muscovy and Russia, the Habsburg lands, Prussia and Germany, the principal Italian and Balkan monarchies, and the Ottoman Empire. Tier 2 adds shorter-lived or smaller realms that clarify a regional story or survive today, such as Galicia–Volhynia, Navarre, Croatia, Monaco and Liechtenstein.
Kyivan Rus’ is treated as shared medieval eastern European history rather than the exclusive predecessor of a single modern state. Galicia–Volhynia records one western Rus’ line of continuity into lands later divided between Poland and Lithuania. Muscovy is shown separately because its direct institutional transition into the Tsardom of Russia in 1547 should not turn the broader Rus’ past into a single Russian state genealogy.
"Europe" is treated as a historical field rather than a hard modern border. The Ottoman Empire is included because its European territory and diplomacy were central to the continent. Byzantium is included even when much of its territory lay in Anatolia. Colonial possessions are not drawn as extra lanes.
One lane does not always mean one state
A lane is an editorial container. Most represent a polity, but some join closely related constitutional phases so the overview stays readable. France, for example, contains West Francia, the pre-revolutionary kingdom, the Bourbon Restoration and the July Monarchy. The gaps between those bars matter. They show that the monarchy was interrupted.
England, Great Britain and the United Kingdom have separate lanes because the Acts of Union created new states. Castile and Aragon remain visible through the composite-monarchy period; the Nueva Planta decrees of 1707–1716 abolished most separate public institutions of the Crown of Aragon and generalized a more Castilian Bourbon framework, but did not erase every regional law in one stroke. Spain also has its own overlapping dynastic phase from 1479. That overlap is deliberate: Isabella and Ferdinand shared a monarchy without erasing the two crowns.
Why this is not a Sankey diagram
Sankey diagrams are built for directed flows with a measurable quantity. Energy, money and material can be divided and recombined, so the width of a stream has meaning. A crown has no comparable conserved quantity. Making the Habsburg line twice as thick as the Tudor line would look informative without saying what was measured.
Every polity bar therefore has the same height. Width encodes time and nothing else. Curved or vertical connectors record a typed relationship: continuity, conquest, dissolution, dynastic union, partition, personal union, composite monarchy, restoration or state union. A dotted conquest line is a historical claim; a fat stream would be an unsupported metaphor.
A dendrogram has a different problem. It assumes a hierarchy and ordinarily places leaves at the same depth. That is useful for hierarchical clustering and phylogenetic trees. European dynastic history is a network with marriages, elective crowns, restorations, cadet branches and people who held several crowns at once. Trees remain useful for a focused genealogy, but they are not the main structure here.
What each mark means
| Mark | Meaning | What it does not mean |
|---|---|---|
| Long neutral bar | A dated institutional phase | Stable borders or an unchanged constitution |
| Coloured inset band | A ruling house assigned to that crown | Unbroken biological descent or unified family policy |
| Dot and short line | A selected monarch and the duration of the reign | A complete list of every ruler |
| Dashed connector | A personal union, dynastic union or composite monarchy | A single merged state |
| Solid connector | Continuity or a constitutional state union | Universal agreement about legal succession |
| Dotted connector | Partition, conquest or dissolution | A judgment about legitimacy |
The data model
The original prototype stored a monarch directly inside one monarchy. That breaks as soon as the same person holds two crowns. James VI and I should be one person with a Scottish reign and an English reign, not two people who happen to share a name.
The current dataset separates six things:
polity: the named lane and its editorial summaryphase: a dated period when that polity or monarchical institution existedhouseandrule: a dynasty plus its dated association with a crownpersonandreign: one human linked to one or more titled reignsrelationship: a typed connection among polity laneseventandsource: dated context and the references used to support it
This model also handles Charles V. He has a Spanish record beginning in 1516, when he assumed the crowns jointly with his mother Joanna, and an imperial record beginning with his election as King of the Romans in 1519. Moving the year line between those dates shows the difference; his papal coronation as emperor occurred in 1530.
Dates and disputed periodization
Many beginnings and endings are conventional. The Roman Empire did not legally split into two unrelated states in 395, even though separate courts and successions became enduring. The western imperial tradition revived by Charlemagne in 800 and the continuous line from Otto I in 962 offer different starting points for what historians later call the Holy Roman Empire. France can be traced from West Francia in 843 or from the Capetian accession in 987. "Spain" can refer to the dynastic monarchy of 1479 or to the more uniform Bourbon order built through the Nueva Planta decrees of 1707–1716.
The project deals with those disagreements in three ways. It records the chosen date, keeps a note explaining the choice, and uses relationship lines to show precursors that would otherwise disappear. The Holy Roman lane starts in 962, while Charlemagne's coronation remains visible as an event in 800.
Years before the Common Era use negative integers in the data. The interface prints them as BCE and never displays a year zero. Continuing phases, house periods and reigns use a null end rather than repeating the publication year; the chart extends them to the snapshot year from the dataset metadata and labels them as continuing to the present.
Sources and verification
The July 2026 publication audit checked current sovereigns against their official institutions and rechecked contested or structurally important claims against official archives, national scholarly encyclopedias and institutional histories. Wikipedia links are retained as broad navigation for many individual rulers and polities, not as the sole authority for the corrections made in this pass. Every selected polity, transition and monarch links to at least one reference from the detail panel.
This is a curated public-history dataset, not a prosopographical database or a substitute for specialist literature. Exact days are reduced to whole years in the visualization, so sub-year accessions and interruptions are stated in notes. Traditional dates such as 843 for the Scottish royal line, 872 for Harald Fairhair and 925 for Tomislav are labelled as conventions rather than presented as secure foundation dates. Source URLs belong to records rather than chart labels so the apparatus can expand without redesigning the visual.
Updates, tests and corrections
The canonical file is data/timeline.json. A build command copies it into the static site, and the validator checks IDs, date ranges, cross-references, required current monarchies, source URLs and minimum coverage. The website itself has no database or server dependency.
The repository's HISTORICAL_AUDIT.md records the July 2026 review standard, major corrections and limits of the annual-scale model. Regression tests preserve consequential fixes such as the English Interregnum, Monaco's French-annexation gap, Majorian's corrected house assignment and the 1917–1922 sequence of imperial collapse.
Corrections are welcome as focused GitHub issues. A useful report names the record, gives the proposed date or wording, and links to a source. Questions of periodization may result in a better note rather than a single "correct" year.
Accessibility and responsive design
All controls are native form elements. Polity labels, phases, house bands, monarch dots and relationship symbols are keyboard-focusable buttons with descriptive labels. Selecting any mark writes the same information into a visible detail panel, so hover is never the only route to the text.
The desktop view uses a horizontal time axis because forty-eight monarchies do not fit as narrow vertical columns. On small screens, the site switches to a focused vertical timeline for one selected polity. Motion is reduced when the operating system requests it, and meaning is paired with labels and line styles rather than colour alone.
License
The data, code and original writing in this repository are available under the MIT License. Linked reference material remains subject to the terms of its publishers.