Anno Domini in the context of "Epoch (date reference)"

The emperor of Japan is the hereditary monarch and head of state of Japan. The emperor is defined by the Constitution of Japan as the symbol of the Japanese state and the unity of the Japanese people, his position deriving from "the will of the people with whom resides sovereign power". The Imperial Household Law governs the line of imperial succession. Pursuant to his constitutional role as a national symbol, and in accordance with rulings by the Supreme Court of Japan, the emperor is personally immune from prosecution. By virtue of his position as the head of the Imperial House, the emperor is also recognized as the head of the Shinto religion, which holds him to be the direct descendant of the sun goddess Amaterasu. According to tradition, the office of emperor was created in the 7th century BC, but the first historically verifiable emperors appear around the 5th or 6th centuries AD.

The role of the emperor of Japan has historically alternated between a largely ceremonial symbolic role and that of an actual imperial ruler. Since the establishment of the first shogunate in 1192, the emperors of Japan have rarely taken on a role as supreme battlefield commander, unlike many Western monarchs. Japanese emperors have nearly always been controlled by external political forces, to varying degrees. Between 1192 and 1867, the shōguns, or their shikken regents in Kamakura (1203–1333), were the de facto rulers of Japan, although they were nominally appointed by the emperor. After the Meiji Restoration in 1868, the emperor was the embodiment of all sovereign power in the realm, as enshrined in the Meiji Constitution of 1889. Since the enactment of the 1947 constitution, the role of emperor has been relegated to that of a ceremonial head of state without even nominal political powers. The emperor is the head of the Japanese honors system, conferring orders, decorations, medals, and awards in the name of the state and on behalf of its people in accordance with the advice of the Cabinet.

Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian or Julian calendar, and are exactly equivalent to the Anno Domini (AD) and Before Christ (BC) notations. The expressions "2025 CE" and "AD 2025" each equally describe the current year; "400 BCE" and "400 BC" are the same year too. BCE/CE are primarily used to avoid religious connotations, by not referring to Jesus as Dominus [Lord].

The Stone Age was a broad prehistoric period during which stone was widely used to make stone tools with an edge, a point, or a percussion surface. The period lasted for roughly 3.4 million years and ended between 4000 BC and 2000 BC, with the advent of metalworking. Because of its enormous timescale, it encompasses 99% of human history.

Though some simple metalworking of malleable metals, particularly the use of gold and copper for purposes of ornamentation, was known in the Stone Age, it is the melting and smelting of copper that marks the end of the Stone Age. In Western Asia, this occurred by about 3000 BC, when bronze became widespread. The term Bronze Age is used to describe the period that followed the Stone Age, as well as to describe cultures that had developed techniques and technologies for working copper alloys (bronze: originally copper and arsenic, later copper and tin) into tools, supplanting stone in many uses.

The Varronian chronology is the commonly accepted chronology of early Roman history named after the Roman antiquarian Marcus Terentius Varro. It is from this chronology that the commonly used dates for the foundation of the city (753 BC), the overthrow of the monarchy (509 BC), the Decimvirates (451–450 BC), the Gallic sack of Rome (390 BC), and the first plebeian consul (366 BC) are derived. The chronology consists of an ordered list of magisterial colleges (eg pairs of consuls) which, in modern times, are regularly assigned to years BC.

The years given by the Varronian chronology prior to 300 BC should not be accepted as absolute dates. Years in the chronology are also demonstrably incorrect and it flows four years prior to actual events by 340 BC. Moreover, Roman historians and antiquarians (most especially Livy and Dionysius of Halicarnassus) also did not all use Varro's scheme. Because both the ordering and absolute position of Varronian years is not well established for this early period, the numeric years derived from it should be taken as "no more than numerical symbols for specific consular years".

The Roman architectural revolution, also known as the concrete revolution, is the name sometimes given to the widespread use in Roman architecture of the previously little-used architectural forms of the arch, vault, and dome. For the first time in Europe, possibly in the world (earlier experiments with arches in Ancient Egypt and Mesopotamia notwithstanding), the potential of these elements was fully appreciated and exploited in the construction of a wide range of civil engineering structures, public buildings, and military facilities. Throughout the Roman Empire, from Syria to Scotland, engineers erected structures using semicircular arches. The first use of arches was for civic structures, like drains and city gates. Later the arches were utilized for major civic buildings bridges and aqueducts, with the outstanding 1st century AD examples provided by the Colosseum, Pont Du Gard, and the aqueduct of Segovia. The introduction of the ceremonial triumphal arch dates back to Roman Republic, although the best examples are from the imperial times (Arch of Augustus at Susa, Arch of Titus).

A crucial factor in this development that saw a trend to monumental architecture was the invention of Roman concrete (also called opus caementicium), which led to the liberation of the shape from the dictate of the traditional materials of stone and brick.

The Sasanian Empire (/səˈsɑːniən/), officially Eranshahr (Middle Persian: 𐭠𐭩𐭥𐭠𐭭𐭱𐭲𐭥𐭩 Ērānšahr, "Empire of the Iranians"), was an Iranian empire that was founded and ruled by the House of Sasan from 224 to 651 AD. Lasting for over four centuries, the length of the Sasanian dynasty's reign over ancient Iran was second only to that of the Arsacid dynasty of Parthia which immediately preceded it.

Founded by Ardashir I, whose rise coincided with the decline of Arsacid influence in the face of both internal and external strife, the House of Sasan was highly determined to restore the legacy of the Achaemenid Empire by expanding and consolidating the dominions of the Iranian nation. Most notably, after defeating Artabanus IV of Parthia at the Battle of Hormozdgan in 224, it began competing far more zealously with the neighbouring Roman Empire than the Arsacids had, thus sparking a new phase of the Roman–Iranian Wars. These efforts by Sasanian rulers ultimately led to the re-establishment of Iran as a major power of late antiquity.

Bulgarian Battle of Versinikia (Bulgarian: Битката при Версиникия; Greek: Μάχη της Βερσινικίας) was a battle fought in 813 AD between the Byzantine Empire and the Bulgarian Empire, near the city of Adrianople (Edirne), in modern-day Turkey.

The Bulgarian army, led by Krum of Bulgaria, defeated the Byzantine forces. Following this defeat, Michael I Rangabe abdicated, with Leo V the Armenian taking the Byzantine throne. The battle further strengthened Bulgarian control in the region after their victory over Nikephoros I two years earlier. After the battle, the Bulgarians controlled the whole region of Eastern Thrace (until the Byzantine–Bulgarian Treaty of 815), with the exception of a few castles that remained in Byzantine control. Krum died on 13 April 814, but his muster of "5,000 iron-plated wagons [ . . . ] to carry the siege equipment" alarmed the Byzantine court to such an effect that they asked for the aid of the Carolingian Emperor Louis the Pious. These large-scale military preparations were Krum's attempt to avenge his failure at the Second Bulgarian Siege of Constantinople one year prior.

Byzantine Anatolia refers to the peninsula of Anatolia (located in present-day Turkey) during the rule of the Byzantine Empire. Anatolia was of vital importance to the empire following the Muslim invasion of Syria and Egypt during the reign of the Byzantine Emperor Heraclius in the years 634–645 AD. Over the next two hundred and fifty years, the region suffered constant raids by Arab Muslim forces raiding mainly from the cities of Antioch, Tarsus, and Aleppo near the Anatolian borders. However, the Byzantine Empire maintained control over the Anatolian peninsula until the High Middle Ages (years 1080s), when imperial authority in the area began to collapse.

The Byzantine Empire re-established control over parts of Anatolia during the First Crusade, and following the sack of Constantinople during the Fourth Crusade, Anatolia became the heartland of the successor states of the Empire of Nicaea and Empire of Trebizond. Following the retaking of Constantinople in 1261, the region gradually passed out of Byzantine control and into the hands of the Ottoman Turks as the empire gradually crumbled. The last Byzantine fortress of Philadelphia fell in 1399, and the last Byzantine presence in the area at Trapezus ended in 1461 with the fall of Trebizond.