Shortly, Leonardo would be called back to Milan at the behest of the French government. While still in Florence, however, he probably made his second attempt to build a flying machine and operate it. (His first attempt was probably made some time in the late 1490s, in Milan.) He designed bird-like gliders and even some machines reminiscent of modern-day helicopters. He based all of his studies on flight and aerodynamics on observations of birds, deftly sketching the creatures' wing movements.
This period marked some of Leonardo's most productive years. Although the Battle of Anghiari would eventually deteriorate, it enjoyed great acclaim during its short existence. Michelangelo was working on what would be the hall's second mural, and although neither would reach completion, artists from all over Italy flocked to observe and compare the paintings while the great masters worked. Had the paintings survived, they would in many ways have defined the style of their times.
Leonardo had also gained immense respect as an engineer by this time: in the midst of his work on the artistic Battle of Anghiari, in 1504, he was called away by the Florentine government to oversee actual fortifications at Piombino. When Leonardo first left Florence for Milan, he seems to have been in search of a city where he could be useful as both an engineer and an artist. Ironically, it was only after his return to Florence, at the age of 50, that he seems to have found the lifestyle he had always desired.