The Lachish Letters are a collection of 18 inscriptions written on fragments of pottery, which were discovered in a guardroom at the city gate of Lachish. They were written during the Babylonian invasion in 587/6 BC, and so provide a rare glimpse into the final days of the Kingdom of Judah. They are inscribed in ink on potsherds (ostraca), and were written in biblical Hebrew similar to that of the Book of Kings and the prose chapters of Jeremiah. Some letters deal with the fate of a prophet.
This one, which seems to have been written shortly before the fall of Lachish to the Babylonians in 586 BC, suggests the fall of nearby Azekah has already happened, from the fact that its fire signals were no longer visible, “We are watching the fire signals of Lachish according to the code which my lord gave us, for we cannot see Azekah”
This is the description of the same event in the Book of Jeremiah, “Then the prophet Jeremiah spoke all these words to Zedekiah, king of Judah, in Jerusalem, when the army of the King of Babylon was fighting against Jerusalem and against all the cities of Judah that were left. Lachish and Azekiah, for these were the only fortified cities of Judah that remained” (Jer 34:6-7)
Israel Museum Link
There are more Lachish Letters in the British Museum in London.