Short answers, pulled from the story.
True cavalry techniques emerged among military elites in ancient states such as Egypt, Assyria, the Hittite Empire, and Mycenaean Greece from the 15th century BC. Archaeological evidence from the Tollense valley confirms horse bones on one of the oldest verified battlefields dating to the 13th century BC.
The last recorded shock force use of chariots in continental Europe occurred during the Battle of Telamon in 225 BC. Chariots persisted for ceremonial purposes like Roman triumphs or racing long after their military utility vanished.
Heavy cavalry became more effective as quality and availability of heavy infantry declined with the fall of the Roman Empire. Shock combat broke loosely formed infantry susceptible to scattering by concentrated charges led by heavily armed horsemen known as milites or knights emerging from late 10th century onwards.
The greatest cavalry charge in modern history took place at the 1807 Battle Eylau where an entire 11,000-strong French cavalry reserve led by Joachim Murat launched a huge charge against Russian infantry lines.
Once front lines stabilized on the Western Front starting early 1915 most cavalry units no longer saw front line action due to trench warfare combinations including barbed wire machine guns and rapid fire rifles. The last massed cavalry encounter on the Eastern Front occurred on the 21st of August 1914 at the Battle Jaroslawice involving thousands of horsemen on both sides.