Please answer a question about the following article about Eritrea:

The Aksumites erected a number of large stelae, which served a religious purpose in pre-Christian times. One of these granite columns, the obelisk of Aksum, is the largest such structure in the world, standing at 90 feet. Under Ezana (fl. 320–360), Aksum later adopted Christianity. In the 7th century, early Muslims from Mecca also sought refuge from Quraysh persecution by travelling to the kingdom, a journey known in Islamic history as the First Hijra. It is also the alleged resting place of the Ark of the Covenant and the purported home of the Queen of Sheba.

Which stelae is considered the largest in the world, standing at 90 feet?
the obelisk of Aksum