The ancient perfect was lost in the Hellenistic period; for 800 years until the introduction of the compound perfect with έχω the aorist played the role of the perfect tense.
This usage is attested in the 1622 grammar of demotic by Girolamo Germano which gives the perfect tense as ἐγραψα. Similar forms are found in the 17th century grammar by Simon Portius and the 1555 grammar by Nikolaos Sofianos.
The compound perfect was introduced via the pluperfect είχον γράψει. Bridget Drinka argues that all such compound perfects in Balkan languages have the same origin, but V. Friedman and BDJ disagree. Within Greek the perfect compounded with ἐχω developed out of the past conditional να είχα γράψει as shown here.