The name of the place is probably to be linked to the expression (in Lombard language) cà merlada, that is "house with battlements". According to Cesare Cantú the first settlement dates back to a fort erected during the wars between the Romans and the Insubri. [without source] The ruins were found and rebuilt by Luitprando, Gothic king. [who? maybe King Liutprand? but he was Lombard, not Gothic...] But its last reconstruction was made by Frederick Barbarossa who erecting new crenellated walls gave the place the name it still bears today.

Translated from Wikipedia