New this week Factual error: At the end of the song "God help the outcasts", Esmeralda bathes in the sunlight of the rose window. Seen from above, the projected light forms a circle on the church-floor. As the rose window is circular itself, and the church-floor is perpendicular to the church-wall, this is only possible when the sun is at exactly 45° above the horizon (the projection would be an ellipse otherwise). However, the Feast of Fools was held at the end of December or the beginning of January, and in this specific case on January 6 1482, according to the original manuscript of Victor Hugo. The highest point the sun reaches in Paris around that day is maximally 20°, even when taking care of the Gregorian Calendar Reform in 1582. Also, the rose window is not exactly southward, which means the sun will have even lower altitude when shining straight through it. Thus, there's no way the sunlight could form a circle on the church-floor around that day.
Factual error: After Phoebus distracts the guards to stop them from chasing Esmeralda, we see the goat smoking a pipe to give the appearance of a beggar. Tobacco (and consequently, smoking pipe) wasn't introduced in Europe for at least another century, as it's a plant native to the Americas.