Short answers, pulled from the story.
Renaissance architecture originated in Florence in the early 15th century. Filippo Brunelleschi (1377-1446) is the architect most credited with bringing it about, working alongside Leon Battista Alberti (1402-1472). Both developed the principles of symmetry, proportion, and geometry drawn from ancient Roman models.
Renaissance architecture is defined by symmetrical plans based on modular proportions, semicircular arches, hemispherical domes, classical orders of columns and pilasters, and precisely carved mouldings and details. Façades are organized around a vertical axis, with regular repetition of window openings, and walls are typically rendered or faced in finished ashlar masonry.
Brunelleschi's dome covers the central space of Florence Cathedral, which had been left without a roof since the 14th century. It is supported by eight large ribs and sixteen internal ones holding a brick shell laid in a herringbone pattern, drawing structural inspiration from the ancient Pantheon in Rome. The dome was a civic undertaking in which eight different quarters of the city each built one of its eight segments.
Alberti wrote De re aedificatoria in 1450, which in 1485 became the first printed book on architecture. His Basilica of Sant'Andrea in Mantua was the first Renaissance building to fully integrate the plan with the façade, and he introduced the use of large scrolls to link different roof heights, a device that became a standard feature of church façades across Europe.
Palladio is described as the most influential architect of the whole Renaissance because his 1570 book I quattro libri dell'architettura, published in Venice, was widely reprinted and spread Renaissance ideas across Europe. His distinctive approach, looking to classical temples rather than Roman civic monuments, produced the Palladian arch motif and buildings like the Villa Capra that were widely imitated.
Renaissance architecture spread through Italian architects working abroad, such as Aristotele Fioravanti in Russia and Sebastiano Serlio in France, and through printed architectural treatises. Non-Italian architects also studied in Italy and brought ideas home, including Inigo Jones in England and Philibert de l'Orme in France. Each country adapted the style to local traditions, producing distinct regional forms such as Plateresque in Spain and Amsterdam Renaissance in the Dutch Republic.