CONSTRUCTION OF HOLY KAABA THE HOUSE OF ALLAH!
The elder son of Ibrahim[Alaihis salam] i.e. Ismail[Alaihis salam] settled in Hijaz. And the Younger son ISHAQ[ALAIHIS SALAM] in SYRIA.
Hijaz in those days was thinly inhabited region in Arabia, while Syria and Yemen were thickly populated countries. The trade and commerce were carried on between these distant parts through Hijaz. Caravans of traders and businessmen constantly passed enroute this inhabited part of Arabia. Allah ordained Hazrat Ibrahim[Alaihis Salam] to find out a place and build a house for His worship in this region. He and His son Ismail[Alaihis salam] jointly built the House called the Kaaba or BAIT ULLAH i.e. The House of Allah.