The English language is divided into three historical versions, each of which is significantly different from the other to the point that it is considered its own language. The first recorded use of English as a language dates back to about 450; it developed from a Germanic language spoken by the Anglo-Saxons who settled in England. The most famous literary work written in Old English is Beowulf. If you try to read Beowulf in its original form, you probably won't get very far. To a Modern English speaker, it will seem like a foreign language—which, indeed, it is.
Around 1100, the language changed significantly due to the Norman invasion of England. This resulted in a huge influx of French words into the vocabulary. These mingled with the Anglo-Saxon words to create the language we call Middle English. A representative literary work written in Middle English is Chaucer's Canterbury Tales. You might have better success trying to read Chaucer in the original. Here are the first two lines of "The Prologue" to Canterbury Tales.
Whan that Aprille with his shoures soote,
The droghte of March hath perced to the roote,
The bold letters indicate a separate syllable. This translates roughly to: When April with its sweet showers has pierced the drought of March to the root. As you can see, Middle English had many word endings that Modern English doesn't have. Many of the silent letters in Modern English spellings were pronounced in Middle English.
By 1500, the language changed again. Language is constantly morphing, but with the advent of the printing press, the language stabilized, and relatively little alteration has occurred since then. The language we speak today is still the language of Shakespeare and the King James Bible, namely Modern English. People often think of words such as "thee" and "thou" as "Old English," but in fact, those archaic terms are part of the language we still speak in the twenty-first century. Modern English has become simplified from its Germanic and Old English roots, having dropped many of the inflections that it used to have.