I thought it was really important to set the time-travelling scenes authentically so researched assiduously all the places that Dan and Sara travel to.
Ancient Rome is as ancient Rome was -- Circus Maximus, the forum and and even the street layout is described as it was.
In Florence with Leonardo da Vinci, the same is true and whilst nowadays the only Palio (street horse race) that is run, is in Sienna (I've been to it -- amazing!), Florence used to have one and the detail of the riders and their gonfaloni (districts) is an accurate potrayal, though I've put a twist on some of the detail.
And the names of the riders create a bit of fun -- Bertruso Festi who rides the winning horse, anagrammatically is "sure to be first"!