Legend has it that, after leaving the village of Vaiamonte, the Master and his Knights were seeking a place to settle near the borders with the Moors when they saw two eagles on a tree.
When they began to build the castle, on the other side of the Avis stream, the knightly friars noticed that little progress had been made. Every morning the building material and tools were exactly on the opposite side where they had been left.
Days and days went by and work was not advancing because the tools and the building materials kept on turning up on the other side of the river. Startled and unaware of how this happened, they decided to stay awake all night to find out who the intruders were that carried things to the other river bank. Eventually, they discovered that it were the eagles, which increased in number, that carried things to the other side. This was taken as a good omen and on 15th August they began the settlement of the place exactly where the town of Avis was established as a tribute to the said birds. These were forever remembered in the coat arms of the town, which also exhibits a cross on a silver background with endings in fleur-de-lis alluding to the Military Order of Calatrava.