How did intermarriage make some coats of arms more complicated?

In heraldry, intermarriage significantly complicates coats of arms through the process of marshaling, specifically when families marry "heraldic heiresses"—women who have no brothers and thus pass their paternal arms to their children.12

When an individual inherits arms from an heraldic heiress, they are entitled to quarter their mother’s arms with their father’s, typically placing the father’s arms in the first and fourth quarters and the mother’s in the second and third. Over generations, families that repeatedly marry heraldic heiresses can accumulate a vast number of quarters, leading to highly complex shields.1

This complexity can escalate further through "grandquartering," where a single quarter is itself subdivided into multiple smaller coats of arms, as seen in the intricate Cameron-Ramsay-Fairfax-Lucy family arms. While some displays may feature dozens or even hundreds of quarters to represent centuries of marriage connections, these are often considered artificial, as they may include the arms of wives who were not heiresses.1