The book of Lamentations (Eikhah in Hebrew), read in synagogue on Tisha b’Av, consists of five chapters. Four of them are structured as alphabetical acrostics; that is, each verse starts with a different letter of the Hebrew alphabet starting with aleph and proceeding in order. In three of these chapters, however, one letter is out of place: the letter peh proceedes ayin—the equivalent of p preceding o. Mitchell First suggests a possible explanation:
In 1976, a potsherd was discovered at Izbet Sartah in Western Samaria, dating to about 1200 BCE. The potsherd had five lines of Hebrew writing on it, one of which was an abecedary (an inscription of the letters of the alphabet in order). In this abecedary, the peh preceded the ayin. There is a scholarly consensus that Izbet Sartah was an Israelite settlement in this period. . . .
[In all other] abecedaries . . . that have [subsequently] been discovered in ancient Israel, dating from the period of the Judges and the First Temple and spanning the letters ayin and peh, peh precedes ayin in every one! . . . [T]hese abecedaries come from different regions in ancient Israel, not merely from one limited area. All of this suggests that peh preceding ayin was the original order in ancient Israel.
Read more on Jewish Link: http://jewishlinknj.com/index.php?option=com_content&view=article&id=8795:the-unusual-pe-preceding-ayin-order-in-the-acrostics-of-the-book-of-eikhah