Ius in Anguilla (Sauce for Eels) is a traditional Ancient Roman recipe for a classic sauce of pepper, lovage, aniseed, celery seeds, sumac, mint and dates in a honey, vinegar, stock, olive oil, mustard and wine base that's intended to be served with poached moray eel. The full recipe is presented here and I hope you enjoy this classic Ancient Roman version of: Sauce for Eels (Ius in Anguilla).
Ius in anguilla: piper, ligusticum, apii semen, anethum, rhus Syriacum, caryotam, mel, acetum, liquamen, oleum, sinape et defritum.
Translation
Sauce for Eels: [Combine] pepper, lovage, celery seeds, anise, Syrian sumac, dried mint, dates, honey, vinegar, liquame, olive oil, mustard and defrutum. [Bring to a boil and pour over the eels.]
Modern Redaction
Though the Romans loved it, moray eel is not much consumed these days. However, this sauce works well with other types of eels and fish such as ling.
Combine the black pepper, lovage (or celery) seeds, aniseed, celery seeds, mustard powder, mint and sumac in a mortar. Pound to grind then add the dates and pound again. Mix in the honey, white wine vinegar, fish stock defritum and olive oil then turn into a saucepan. Bring to a boil, reduce to a simmer and cook gently for 20 minutes, or until thickened.