|Covid-19|March 2 – Siege of Rome: The Ostrogoth army (45,000 men) under King Vitiges begins the siege of the capital. Belisarius conducts a delaying action outside the Flaminian Gate; he and a detachment of his bucellarii are almost cut off.
Vitiges sets up seven camps, overlooking the main gates and access routes to the city, in order to starve it out. He blocks the Roman aqueducts that are supplying Rome with water, necessary both for drinking and for operating the corn mills.
March 21 – Vitiges attempts to assault the northern and eastern city walls with four siege towers, but is repulsed at the Praenestine Gate, known as the Vivarium, by the defenders under the Byzantine generals Bessas and Peranius.
April – The Goths capture the Portus Claudii at Ostia; the harbor is left unguarded by the Romans. Belisarius is forced to unload his supplies at Antium (modern Anzio); he sends urgent messages for reinforcements to Constantinople.
April 9 – Belisarius receives his promised reinforcements: 1,600 cavalry, mostly of Hunnic or Slavic origin and expert bowmen. He starts, despite shortages, raids against the Gothic camps and Vitiges is forced into a stalemate.
June – In Rome, famine brings the city to despair; Belisarius sends his secretary Procopius to Naples for more reinforcements and supplies. Vitiges arranges a three-month armistice for Gothic envoys to travel to Constantinople.
November – Belisarius brings his long-awaited reinforcements, namely 3,000 Isaurians and 1,800 cavalry embarked in Ostia, along with a supply convoy, safely to Rome. The Goths are forced to abandon the Portus Claudii.
December – Belisarius sends John "the Sanguinary" with a force of 2,000 men towards Picenum, to plunder the east coast of Italy. He arrives at Ariminum (Rimini), where he is welcomed by the local Roman population.
December 27 – The construction of the Hagia Sophia in Constantinople (begun in 532) is completed.
Battle of Camlann: King Arthur fights his last battle against the forces of his rebellious son (or nephew) Mordred, and is mortally wounded (according to the 10th-century Annales Cambriae).
Spring – At the Battle of Scalas Veteres in Africa, Byzantine troops under Germanus crush a large-scale mutiny. Stotzas, leader of the rebellion, flees with a handful of followers to Mauretania.
Eastern Wei sends an advance guard of three army columns through the Tong Pass, to attack Western Wei. The Western army under Yu-Wen Tai defeats one of the columns while the others retreat. Yu-Wen follows up, but runs into the main Eastern army (200,000 men). The Westerners are pushed back through the pass, and the Eastern army emerges from the mountains. Unexpectedly they are charged in the flank by 10,000 Western cavalry, and 6,000 Easterners are killed and 70,000 captured.
John Cottistis starts a short-lived rebellion against Justinian I. He is declared emperor at Dara, but is killed four days later by conspiring soldiers.
Yaxchilan captures the ajaws of Bonampak, Lakamtuun, and Calakmul at the outset of the First Tikal-Calakmul War.
The Aqua Virgo aqueduct is destroyed by the Goths; they try to use the underground channel as a secret route to invade Rome.
March 29 – Pope Vigilius succeeds Silverius as the 59th pope, when the latter is deposed by Belisarius at the order of Justinian I.
Second year of worldwide famine, a consequence of the Extreme weather events of 535–536.
Agilulf, bishop of Metz (approximate date)
Chen Chang, prince of the Chen Dynasty (d. 560)
Gong Di, emperor of Western Wei (d. 557)
Wu Cheng Di, emperor of Northern Qi (d. 569)
Arthur, king of Britain (approximate date)
Fortunatus, bishop of Todi
Gartnait I, king of the Picts
Husi Chun, general of Northern Wei (b. 495)
Isidore of Miletus, Byzantine architect
John Cottistis, Byzantine usurper
Maine mac Cearbhall, king of Uí Maine (or 531)
Mordred, son (or nephew) of Arthur (approximate date)
December 2 – Pope Silverius
Vigor, bishop of Bayeux
Year 537 (DXXXVII) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Second year after the Consulship of Belisarius (or, less frequently, year 1290 Ab urbe condita). The denomination 537 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.