Tang dynasty astronomer, mathematician, and Buddhist monk Yi-xing and government official Liang Ling-zan combine Zhang Heng's water-powered celestial globe with an escapement device in 723.

The result is allegedly the world's first water powered mechanical clock.

Yi-xing has also calculated the number of possible positions on a go board, though without a sign for zero he has difficulties expressing the number.

Usa, a city in modern Oita ken (prefecture), northern Kyushu, Japan, begins to develop around the site of the first and most famous of shrines dedicated to the Shinto god Hachiman, Usa Hachiman Shrine, which dates to about 717–724.

The taxation system that had been introduced in Japan by Empress Jitō in the late seventh century has begun to malfunction.

To motivate new cultivation and compensate for decrease of tax revenue, an initiative passed in 723 by Prince Nagaya allows people to possess the fields newly placed under cultivation for a maximum of three generations.

In the fourth generation, the right of possession is to transfer to the national government.

The long reign of Vijayaditya, who had succeeded his father, Vikramaditya, to the Chalukya throne in 696, has been marked by general peace and prosperity.

He has fought against the Pallavas and extracted tributes from Parameshwar Varma V, and built a number of temples.

Pelagius and the Birth of the Reconquista

Pelagius (Pelayo), leading an alliance of Asturian and Cantabrian mountaineers, along with Visigothic Spaniards, launches a counteroffensive against the Muslims, marking the beginning of what will later be called La Reconquista.

His victory at Covadonga (722 CE) establishes the Kingdom of Asturias, the first Christian stronghold in post-Visigothic Iberia. From this small, mountainous refuge, Pelagius founds a dynasty of Iberian monarchs who, over the next nearly eight centuries, will gradually reclaim the entire Iberian Peninsula from Muslim rule, culminating in the fall of Granada in 1492.

Winfrid-Boniface has labored in Hesse, Thuringia and Frisia for five years, and in late 722 had been recalled by Gregory to Rome to be consecrated as a bishop; the pope, who has greatly encouraged the Christianizing of Germany, also had given him the name Boniface, by which he is henceforth to be known.

The pope also provides him with a collection of canons (ecclesiastical regulations) and letters of recommendation to such important personages as Charles, master of the Frankish kingdom, whose protection is essential to Boniface's success.

He returns to his missionary work in Germany the following year.

Veneration of sacred groves and sacred trees is found throughout the history of the Germanic peoples and were targeted for destruction by Christian missionaries during the Christianization of the Germanic peoples.

On his arrival in northern Hesse, Boniface, cloaked by the pagan awe of Charles's name, fells the sacred oak tree dedicated to the Germanic god Thor at Geismar near the present-day town of Fritzlar.

He builds a chapel from its wood at the site where today stands the cathedral of Fritzlar.

The felling of Thor's Oak, an ancient tree sacred to the Germanic tribe of the Chatti, is commonly regarded as the beginning of German Christianization.

Chinese Buddhism reaches its greatest heights during the glorious and tolerant period of the Tang dynasty at its zenith, and Islam, Manichaeanism, Judaism, Zoroastrianism and Nestorian Christianity all enter China.

East Central Europe (724–735 CE): Saxon Territorial Expansion, Formation of Slavic States, and Avar Continuity

Between 724 and 735 CE, East Central Europe—encompassing Poland, Czechia, Slovakia, Hungary, and those portions of Germany and Austria lying east of 10°E and north of a line stretching from roughly 48.2°N at 10°E southeastward to the Austro-Slovenian border near 46.7°N, 15.4°E—continued its transition toward more defined medieval political structures. Saxon tribes consolidated and expanded their territories, reinforcing their status as a powerful regional force. Emerging Slavic principalities in Bohemia and Moravia strengthened their governance structures, while the Avar Khaganate maintained political stability within its Carpathian heartland. Thuringia's continued autonomy underscored ongoing Merovingian fragmentation, marking an important transitional period toward the Carolingian ascendancy.

Political and Military Developments

Saxon Eastward Expansion

• Saxon tribes continued their territorial consolidation east of the Elbe, expanding deeper into eastern Germany and parts of western Poland. Their increased presence reshaped political alignments, trade networks, and cultural interactions with neighboring Slavic principalities and Thuringia.

Strengthening of Slavic Principalities

• Bohemian and Moravian political structures matured significantly, transitioning from loosely organized tribal federations into clearly defined early medieval states with strengthened leadership and more stable territorial boundaries.

Thuringian Autonomy Amid Frankish Decline

• Thuringian dukes maintained effective political independence from weakened Merovingian royal power, further exemplifying the fragmentation and localized rule characterizing this era.

Avar Stability and Diplomatic Relations

• The Avar Khaganate remained diplomatically stable, cautiously balancing relations with expanding Saxon and Slavic powers while maintaining firm internal cohesion in the Carpathian Basin.

Economic and Technological Developments

Continued Economic Prosperity and Trade Networks

• Active regional trade persisted across East Central Europe, connecting Saxon, Slavic, Bavarian, Thuringian, Avar, and Frankish communities. Trade included agricultural produce, metals, textiles, ceramics, livestock, and luxury goods.

Fortified Settlement Expansion

• Communities across Saxon, Slavic, and Avar territories continued expanding their fortified settlements, reflecting greater political stability, population growth, economic prosperity, and technological sophistication.

Cultural and Artistic Developments

Diffusion of Saxon Cultural Elements

• Saxon expansion disseminated distinct Germanic cultural traits widely across eastern Germany and neighboring regions, influencing artistic production, jewelry styles, pottery, burial customs, and weaponry.

Further Definition of Slavic Regional Identities

• Bohemian and Moravian communities further refined their distinctive Slavic cultural identities, visible archaeologically through differentiated ceramics, jewelry, and fortified settlement designs.

Continued Influence of Avar Artistic Traditions

• The Avars maintained their artistic influence across the region, particularly in sophisticated metalwork, jewelry, equestrian equipment, and decorative arts.

Settlement and Urban Development

Saxon Urban and Rural Growth

• Saxon settlements expanded eastward and became increasingly fortified and economically productive, laying the groundwork for medieval urban centers in eastern Germany and adjacent areas of Poland and Czechia.

Development of Slavic Administrative Centers

• Emerging urban and political centers within Bohemia and Moravia expanded notably, reflecting political maturity, demographic growth, and growing economic activity.

Stability and Prosperity in Thuringia and Bavaria

• Bavarian and Thuringian settlements, particularly significant towns such as Regensburg, enjoyed sustained stability, benefiting from minimal external threats and vibrant regional trade networks.

Social and Religious Developments

Strong Saxon Tribal Leadership

• Saxon social hierarchy remained robust under influential warrior elites, whose political and military strength facilitated territorial expansion, economic growth, and regional dominance.

Consolidation of Slavic Hierarchies

• Slavic leadership in Bohemia and Moravia continued to centralize, fostering clearer political structures, strengthened defenses, and improved internal governance.

Stable Avar Social Structures

• Avar society retained its structured, hierarchical organization under a strong nomadic elite leadership, ensuring continued internal stability and diplomatic efficacy.

Long-Term Consequences and Historical Significance

The era 724–735 CE marked significant steps toward the medieval political landscape of East Central Europe. Saxon territorial growth, consolidated Slavic principalities, sustained Thuringian independence, and stable Avar control collectively set the foundations for enduring political entities, cultural identities, and economic patterns influencing the region’s medieval trajectory profoundly.

Christian religious pictures and relics as objects of veneration in worship services is the defining issue of the era, as East Roman Emperor Leo III, in undertaking a set of civil reforms, begins to speak out publicly in 726 against the use of sacred pictures, and orders the destruction of the image of Christ at the Chalke palace in Constantinople.

Popular revolts against iconoclasm break out in the late 720s in the Cyclades, Naples, Venice, Rome, and elsewhere.

Many Greek theologians, including John Damascene, react to the new policy by developing an elaborate theory and defense of holy images and their place in worship.

Leo, proclaiming Iconoclasm the official policy of the empire in 730, orders the removal and destruction of sacred pictures in churches.

His policies meet particularly strong opposition from monastic circles.

Pope Gregory II also strongly rejects his efforts to impose Iconoclasm upon areas of Italy under imperial control.

The two outbreaks of Iconoclasm in the Empire during the eighth and ninth centuries are unusual in that the use of images is the main issue in the dispute, rather than a byproduct of wider concerns.

Iconoclasm in Christianity has generally been motivated by a literal interpretation of the Ten Commandments, which forbid the making and worshiping of "graven images".

As with other doctrinal issues in the Byzantine period, the controversy is by no means restricted to the clergy, or to arguments from theology.

Iconoclasm seems to have been supported by many from the East of the Empire, and refugees from the provinces taken over by the Muslims.

The continuing cultural confrontation with, and military threat from, Islam probably has a bearing on the attitudes of both sides.

It has been suggested that their strength in the army at the start of the period, and the growing influence of Balkan forces in the army (generally considered to lack strong iconoclast feelings) over the period may have been important factors in both beginning and ending imperial support for iconoclasm.

Eastern Southeast Europe (724–735 CE): Iconoclasm and Religious Controversy

Settlement and Migration Patterns

Continued Stability and Cultural Cohesion

From 724 to 735 CE, demographic stability continued within Eastern Southeast Europe, particularly among the well-established Slavic and Bulgar populations. Cultural integration remained strong, supporting regional identity despite broader religious and political upheavals.

Political and Military Developments

Arab Threat Management

The Byzantine Empire remained vigilant against intermittent Arab threats but enjoyed a brief respite following previous successful defenses. Military fortifications continued to be maintained, securing vital regions against external incursions.

Economic and Technological Developments

Economic Stability Through Defensive Strategies

Economic conditions remained stable, supported by continued strategic investment in defense infrastructure. Fortifications and defensive preparations around major urban centers safeguarded vital trade routes and agricultural productivity.

Cultural and Artistic Developments

Religious and Cultural Conflict: Iconoclasm

The defining issue of this era was the Iconoclast controversy, initiated by Emperor Leo III, who publicly condemned the veneration of religious images beginning in 726. Leo's order to destroy the image of Christ at Constantinople's Chalke palace symbolized the policy's aggressive implementation.

Artistic Resistance and Theological Defense

Popular revolts erupted throughout the Byzantine territories, including the Cyclades, Naples, Venice, and Rome, illustrating widespread opposition to iconoclasm. Prominent theologians, notably John Damascene, articulated detailed defenses of religious imagery, firmly establishing theological arguments in support of icons.

Social and Religious Developments

Institutional Division: East vs. West

Emperor Leo III formally declared Iconoclasm as imperial policy in 730, mandating the removal and destruction of sacred images in churches. His stance faced vehement opposition from monastic communities and the broader ecclesiastical establishment, intensifying the rift between imperial authority and religious practice.

Opposition from the Papacy

Pope Gregory II notably rejected Leo III's iconoclastic directives, particularly in regions of Italy under Byzantine influence, underscoring the growing ecclesiastical divide between Eastern Orthodoxy and Western Christianity. This controversy contributed significantly to long-term doctrinal and institutional divergences between East and West.

Impact of Cultural and Military Context

Iconoclasm’s support was particularly pronounced among military and administrative groups from the Empire’s eastern provinces, many influenced by cultural confrontations and threats from Islam. Conversely, Balkan military contingents, generally less supportive of iconoclasm, played a role in influencing imperial attitudes over the era.

Long-Term Consequences and Historical Significance

The era from 724 to 735 CE was deeply marked by the Iconoclast controversy, reshaping Byzantine society, theology, and politics. The religious conflicts that emerged during this period established critical ideological and ecclesiastical distinctions, profoundly influencing the historical development of Eastern Orthodoxy and its complex relationship with Western Christianity.