Ancient writers on the Latin language had the concept of ‘reconstruction’ of words which existed in earlier stages of the language. In some ways this was similar to modern notions of reconstruction, in others different. In this article I show how they used concepts of relationships of sounds between older and classical Latin, and between Latin and other languages, to come up with their reconstructions. I will also show that these reconstructions were considered to have once existed, to the extent that they could be treated as real words in lexica.