| Ancient Greek and Egyptian medicine were both very familiar with diabetes. They didn't know what it was, what caused it or how to treat it, but they were aware of the symptoms and what it meant. Allegedly the correlation was made when it was noticed that ants tended to congregate around pools of urine left by both people and animals with diabetes.
Indeed, the term 'diabetes mellitus' means 'sugary fountain', which refers directly to its most obvious symptom and its method of discovery. It's only been in the last 50 years or so that we've actually moved away from urine testing, and we still use it for ketones.
A lot of people don't realise that the ancient world was familiar with a lot of diseases which we wouldn't have credited them with, and although frequently the causes of disease remained a mystery, they could accurately diagnose and even treat serious conditions. For instance, treppaning actually works in relieving certain permenant headaches. Much ancient Greek medical knowledge was largely lost in Europe following the collapse of the Roman empire and to be honest we have to be grateful to the Arabs for preserving vast tracts of medical knowledge during the Dark Ages.  | 
