The earliest definite written examples of Frisian are from approximately the 9th century AD. A few examples of Runic inscriptions from the region are probably older and possibly in the Frisian language.
Old English is arguably more closely related to Frisian than any other language; even modern English bears some resemblance if one ignores the French vocabulary grafted on to English during the Middle Ages. A rhyming couplet demonstrating this is in common circulation:
Good butter and good cheese
Is good English and good Fris
The first line of this verse is pronounced essentially identically in both languages.