It was only a few years after the city of Siena had decided to abandon the massive expansion and redesign of their cathedral in 1355 that Florence decided to greatly expand theirs. A plan for the dome of Florence Cathedral was settled by 1357. However, in 1367 it was proposed to alter the church plan at the east end to increase the scale of the octagonal dome, widening it from 62 to 72 braccia, with the intent to further surpass the domes of Pisa and Siena, and this modified plan was ratified in 1368, under Master of Works Francesco Talenti. The construction guilds of Florence had sworn to adhere to the model of the dome created in 1367, with a "quinto acuto" pointed profile, but the scale of this new dome was so ambitious that experts for the Opera del Duomo, the board supervising the construction, expressed the opinion as early as 1394 that the dome could not be accomplished. Discussion in the fourteenth century revolved primarily around the cost of the project, and secondarily about the style. The enlarged dome would span the entire width of the three aisled nave, just 2 meters less than that of the Roman Pantheon, the largest dome in the world. And because the distances between the angles of the octagon were even farther apart at , the average span of the dome would be marginally wider than that of the Pantheon. At 144 braccia, the height of the dome would evoke the holy number of the Heavenly Jerusalem mentioned in the Book of Revelation. By 1413, with the exception of one of the three apses, the east end of the church had been completed up to the windowed octagonal drum but the problem of building the huge dome did not yet have a solution. In 1417, with the drum completed, the master builder in charge of the project retired and a competition for plans to build the dome was begun in August 1418.
