The font is something of an enigma. It is as far as is known, unique. The shape and general dimensions suggest an eastern origin, possibly Byzantine. It has been suggested that the font arrived in St Mary's at the time of the Second Crusade in the 12th century. However, the font is almost certainly at least a century older than this.

The lions and monkeys around the base of the font are very finely carved and contrast strangely with the four figures around the top of the font which appear to be misshapen and poorly proportioned possibly as a result of recarving by another hand.

The Latin inscription around the top reads: "You give me life-giving water from Jerusalem, making me such as I am, beautiful and distinctive."

More earthily, the Latin inscription around the base of the bowl reads: "You are unwise if you do not run away; look, there are lions."