An ugly stone?

An ugly piece of limestone with some scribbled lines of text in black ink - that would be the first impression of Leiden AAL 146a (on the right), as this object is officially known. Not ‘known’ as in ‘famous’; it is not on display, but hidden in the Rijksmuseum van Oudheden's storeroom.

However, the object becomes more interesting when combined with its uninscribed counterpart: AAL 146b (on the left). It seems to match precisely with the shape of ‘a’, like the lid of a pot - almost literally, since ‘b’ is clearly a cover for ‘a’ and its textual content.