If Rammas Echor was the second spell you cast in a turn, its first ability won't trigger that turn.

A creature attacks alone if it's the only creature declared as an attacker during the declare attackers step (including creatures controlled by your teammates, if applicable). For example, exalted won't trigger if you attack with multiple creatures and all but one of them are removed from combat.

Spells that were cast before Rammas Echor, Ancient Shield entered the battlefield count. If Rammas Echor was the first spell you cast in a turn, the next spell you cast that turn is your second spell.