The like of which were not created in the land,
meaning, there had been none created like them in their land, due to their strength, power and their great physical stature.
Mujahid said,
"Iram was an ancient nation who were the first people of `Ad."
Qatadah bin Di`amah and As-Suddi both said,
"Verily, Iram refers to the House of the kingdom of `Ad."
This latter statement is good and strong.
Concerning Allah's statement,
الَّتِى لَمْ يُخْلَقْ مِثْلُهَا فِى الْبِلَـدِ
The like of which were not created in the land,
Ibn Zayd considered the pronoun of discussion here to refer to the pillars, due to their loftiness. He said,
"They built pillars among the hills, the likes of which had not been constructed in their land before."
However, Qatadah and Ibn Jarir considered the pronoun of discussion to refer to the tribe (of `Ad), meaning
that there was no tribe that had been created like this tribe in the land - meaning during their time.
And this latter view is the correct position.
The saying of Ibn Zayd and those who follow his view is a weak one, because if He intended that, He would have said
"The like of which were not produced in the land."
But He said;
لَمْ يُخْلَقْ مِثْلُهَا فِى الْبِلَـدِ
The like of which were not created in the land.
Then Allah says,
وَثَمُودَ الَّذِينَ جَابُوا الصَّخْرَ بِالْوَاد