The biblical pattern - never intermarry. The patriarchs had to marry within their family and not from 'the daughters of the land' (Genesis 24.3 - Isaac's wife; Genesis 27.46 - Jacob's wife).
Why did they have to do this?
Because 'the LORD had said to the children of Israel, "You shall not intermarry with them, nor they with you. Surely they will turn away your hearts after their gods." Solomon clung to them in love, however. It was so, when Solomon was old, that his wives turned his heart after other gods... Solomon did evil in the sight of the LORD, and did not fully follow the LORD, as did David his father' (1 Kings 11.1-6).
