Whats the position of treasure trove in German law? Its a bit strange. There are rules in the Civil Code relating to Schatzfund (section 984).
Wird eine Sache, die so lange verborgen gelegen hat, daß der Eigentümer nicht mehr zu ermitteln ist (Schatz), entdeckt und infolge der Entdeckung in Besitz genommen, so wird das Eigentum zur Hälfte von dem Entdecker, zur Hälfte von dem Eigentümer der Sache erworben, in welcher der Schatz verborgen war.
If a thing is discovered which has remained hidden so long that the owner can no longer be ascertained (treasure), and it is taken in to [sic] possession as a result of the discovery, one half of the ownership is acquired by the discoverer, and the other half by the owner of the property in which the treasure was hidden.
The definition here is very broad. It is just necessary for something to have been hidden (as opposed to lost) for it to be treasure trove. I suppose no-one would take legal action if they find a secret chewing gum cache, though. The division into two halves goes back to Emperor Hadrian.
However, this Civil Code section is rarely applied, because there is something in Land law called Schatzregal, and the Länder also have rules governing the kind of treasure that ends up in museums – I suppose because cultural and educational affairs and thus museums are the matter of the Länder.
Schatzregal has nothing to do with bookcases, as I used to think. There are two words Regal in German, with different etymologies. One means a bookcase, and the other means a sovereign right, usually with some economic value, originally a right of the king or local rules and later a right of the state. This word is related to the English adjective regal. The big Muret-Sanders (Langenscheidt) dictionary translates it as regale, regality, royal prerogative, royalty. Walker’s Oxford Companion to Law says that treasure trove belongs ‘by prerogative right’ to the Crown. The OED doesn’t confirm this meaning of regale; it’s just possible that ‘regalities’ would work, but I think ‘prerogative’ is more widely known. Apparently in the 13th-c. Sachsenspiegel, every treasure that lies deeper in the earth than a plough reaches belongs to the king (see a useful review of a book on the topic, in German, with links).
If something is defined as a Kulturdenkmal (historical monument, but this includes movable property), then Land law will govern. It varies in its definitions and in its results. I have the impression that Schatzregal does not apply in Bavaria and that in Länder where it does apply, treasure trove goes to the Land government without compensation.