When was the Book of Lamentations written?

The common conception is that the Book of Lamentations, which mourns the destruction of first Holy Temple and the ensuing exile of the Jewish nation, was written in reaction to those tragic events. Many paintings depict the prophet Jeremiah, the author of Lamentations, penning the work while in the background Jerusalem and the Temple are going up in smoke.

In actuality, the widely accepted Jewish view is that Lamentations (or at least the bulk of it) was penned years before the actual calamitous events it depicts.

The First Temple was destroyed in the year 423 BCE. Seventeen years earlier, G‑d instructed Jeremiah, "Take for yourself a scroll and write upon it all the words that I have spoken to you concerning Israel and concerning Judah. . . . Perhaps the house of Judah will hear all the evil that I plan to do to them, in order that they should repent, each man of his evil way, and I will forgive their iniquity and their sin."

Jeremiah, who was imprisoned at the time (apparently because King Jehoiakim was tired of listening to Jeremiah's prophecies foretelling the fall of Jerusalem), dictated to his devoted student Baruch ben Neriah three chapters, each chapter consisting of twenty-two verses, each verse beginning with a different letter, following the order of the Hebrew alphabet. These chapters vividly and heart-wrenchingly describe the tragedies and calamities that would befall Judah. The chapters speak in past tense, lamenting these events as if they had already occurred.

Baruch wrote these chapters on a scroll, and, at the prophet's instruction, read them to the people gathered in the Temple. Ultimately, the document was read before the king, Jehoiakim, who upon hearing only the first few verses callously tossed the scroll into the fireplace. 

G‑d then instructed Jeremiah to rewrite the prophecies. Jeremiah again dictated the prophecies to his student, this time adding an additional chapter—one that contained 66 verses, the first three starting with the letter aleph, the next three with a beit, and so on.1

The first three chapters that Jeremiah wrote constitute chapters 1, 2 and 4 of the Book of Lamentations. The sixty-six verse chapter he added is chapter 3 of Lamentations. Chapter 5 – the only chapter that isn't an alphabetical acrostic, though it too contains twenty-two verses – was added by Jeremiah at a later time.

(Chapter 4 was originally composed as a eulogy for King Josiah (Yoshiyahu), Jehoiakim's father.2 Unlike Jehoiakim, Josiah was a truly saintly individual, as the Torah testifies (II Kings 23:25): "Before him there was no king like him, who returned to G‑d with all his heart and with all his soul and with all his might, according to the entire Torah of Moses, and after him no one [of his stature] arose."3)

And indeed, seventeen years later, on the ninth of Av in the year 3338 from creation, the Temple was destroyed and the Jews led into captivity—precisely as Jeremiah had prophesied.4

Ever since, the Book of Lamentations is read every year on the eve of the 9^th of Av.

May G‑d soon comfort us and usher in the time when we will be doubly consoled with the coming of Moshiach and the rebuilding of the Holy Temple.