If there is one event which triggered the start of the Renaissance, which seems improbable, it was perhaps the competition to design the second door of the Baptistry of the Duomo in Florence. The door was to be formed from brass panels corresponding to the first door which had already been built. And artists were invited to submit a panel representing the Sacrifice of Isaac.
Two artists were declared joint winners of the competition, the young Lorenzo Ghiberti, and Filippo Brunelleschi, though the doors were designed by Ghiberti, Brunelleschi seemingly having withdrawn from the process. Both the panels they submitted to the competition survive, can be seen in the Museo Nazionale del Bargello and are illustrated here.
Both panels are remarkable works of art but a comparison between the two shows them stepping between the Medieval and the Renaissance. The difference is most clearly seen in the figure of Isaac, being sacrificed by his father. The figure by Brunelleschi is clearly a medieval figure, flattened and slightly distorted, readily connected to medieval paintings and illustrated manuscript. The figure of Isaac as depicted by Ghiberti has, by contrast, a different derivation. It is a figure which draws from the sculptures of the classical period. It is an idealised, classical image of youthful beauty such as was soon to become a central feature of Renaissance art.
That of course is not the only difference. The approach to perspective is different too, with Brunelleschi presenting the figures as flat cartoons, as if in a Medieval fresco whilst Ghiberti seems to have mastered a different sense of perspective which adds a depth to the scene missing from Brunelleschi.
They are small differences between two compelling images, both of which show the standards to which artists working in florence at the start of the C15 could rise. But if you have to set a single date as a starting point for a new era in art and culture, perhaps 1401 does represent the start of the Renaissance.