Chronology

Chronology is the formal science of arranging events in their order of occurrence. It is the method used to determine the actual temporal sequence of past events. This science is a vital part of periodization, which is the process of dividing history into blocks of time. Chronology is also a fundamental part of the discipline of history. It connects to earth history and the study of the geologic time scale. Scientists use chronology to locate specific historical events in time. This work relies heavily on chronometry, or timekeeping, and historiography, which is the study of historical writing methods.

To determine the age of objects, scientists use several specialized techniques. One method is radiocarbon dating. This process estimates the age of formerly living things by measuring the proportion of the carbon-14 isotope in their carbon content. Another method is dendrochronology, which is the study of tree rings. Scientists correlate various growth rings in wood to known year-by-year reference sequences. These sequences reflect year-to-year climatic variation. Dendrochronology is often used as a calibration reference for radiocarbon dating curves. These different methods help reinforce a chronology through the axiom of corroborative evidence.

Chronology also involves the use of calendars and eras. A calendar is a system for organizing days, while an era is a coherent system of numbered years. An epoch is the specific date, usually a year, when an era begins. For example, Dionysius Exiguus founded the Christian era around the year 500. This era is the most widespread dating system on Earth today. In the past, the Julian calendar was used during the 8th century. Later, after the year 1582, the Gregorian calendar became the standard. These systems allow us to place human events into a predictable, numbered sequence.

Ancient civilizations used different ways to track their own time. The Romans used an era called Ab Urbe condita, or AUC. This translates to "from the founding of the City" of Rome. This era was traditionally set in 753 BC. While Roman historians used it, they often identified years by naming the two consuls in office. Modern historians actually use AUC more frequently than the Romans did. The Iberian historian Orosius used it systematically around the year 400. Later, Pope Boniface IV connected this era to the Anno Domini system around the year 600.

In archaeology, researchers use sequence dating to study prehistory. This is especially important when written chronicles or king lists do not exist. In the late 19th century, archaeologists developed relative chronologies using pottery styles. William Flinders Petrie pioneered a method called seriation in the field of Egyptology. He studied groups of contemporary artifacts found together in graves. By working backwards from known historical phases, he could penetrate Neolithic times. This process involves two phases: classification and typology. Classification creates categories for description, while typology analyzes changes to place artifacts in a sequence.

One of the biggest challenges in chronology is the problem of synchronism. Synchronizing means relating one event to the current time or to other events. Historians often need to synchronize the reigns of different kings. This allows them to compare the history of one region to another. Eusebius wrote a major work called the Chronicon in 325 AD to solve this. He included narrative chronicles for nine kingdoms, such as the Assyrian and Roman kingdoms. He used a long table to show these events in parallel columns. This allowed readers to see which events were contemporaneous.

Eusebius used the Anno Mundi era to place all these events on one scale. This era dated events from the supposed beginning of the world. Based on his computation from the Book of Genesis, this occurred in 5199 BC. His work was widely used in the medieval world to establish historical dates. Later, the scholar Joseph Scaliger reconstructed lost parts of this history. Scaliger lived from 1540 to 1609 and wrote two major works. These were De emendatione temporum in 1583 and Thesaurus temporum in 1606. His work remains a foundation for modern ancient world dating.

Scaliger's contributions changed how we view time. He invented the concept of the Julian Day. This is still used today as the standard unified scale for historians and astronomers. Beyond literary methods, scientists can also synchronize history using astronomical events. For example, the Eclipse of Thales is described in the writings of Herodotus. This eclipse can help date the Lydian War because it happened during a major battle. By using both written records and scientific observations, chronology provides a reliable map of human history.