Albert Barnes Commentary Nehemiah 2:19

"But when Sanballat the Horonite, and Tobiah the servant, the Ammonite, and Geshem the Arabian, heard it, they laughed us to scorn, and despised us, and said, What is this thing that ye do? will ye rebel against the king?" — Nehemiah 2:19 (ASV)

Geshem the Arabian - The discovery that Sargon populated Samaria in part with an Arab colony explains why Arabs would have opposed the fortification of Jerusalem.