It used to be rather the case that what we knew about the Picts was how little we knew about then in so far as they left little in the way of literary remains other than a few inscriptions and that our information came almost entirely from the records of other peoples.
Archaeological evidence in the surviving and striking standing stones and instances of treasure trove is central to such understanding as we have of the time beforre Pictland yielded to the emergence of what became Scotland.
That picture has now been modified as canbe seen from the Wikipedia account of the Picts, but it also demonstrates the numbers of questions that remain without clear answers in respect of the history and culture of the Picts. It can be seen at Picts
The discovery of another toppled Pictish standing stone, this time in the kirkyard at Old Kilmadock near Doune in Perthshire, adds not only another fine example of Pictish art to the total already known but raises new questions of its own because of where it was found and its design and Ogham inscription. Dated to between 500 and 700 it is in what was then both a geographical border region as well as a cultural one between Pictish and Irish cultures.
There are informative articles about the discovery from The Scotsman at Remains of Pictish period cross with bird carvings uncovered in Scottish kirkyard, from Live Science at Rare medieval script discovered on stone carved by Scotland's 'Painted People', and from Ancient Origins at Ancient Pictish Cross Stone Slab ‘Complicates History’