42 Then one poor widow came and threw in two mites, which make a quadrans. 43 So He called His disciples to Himself and said to them, “Assuredly, I say to you that this poor widow has put in more than all those who have given to the treasury; 44 for they all put in out of their abundance, but she out of her poverty put in all that she had, her whole livelihood.” (Mark 12:42-44, NKJV)
According to Michael Markowitz of the Ancient Numismatic Society of Washington, the widow’s mite is most likely to be the common prutah (plural: prutot) issued by Alexander Jannaeus. These coins were snall copper coins, weighing about two grams, and showing a pair of entwined cornucopiae (“horns of plenty,” a universal symbol of abundance).
Source: Michael Markowitz
Although these coins were struck before 76 BCE (and therefore, would have been almost a hundred years old when Jesus saw them in the Temple circa 30 CE), it should be remembered that in the ancient world, coins could remain in circulation for centuries long after the governments that issued them were only a distant memory (i.e., they remained in circulation until they were totally worn out).
According to Wikipedia, a loaf of bread at that time was worth about 10 prutot (plural of prutah).
For details on the widow’s mite, you can read this article written by Mr Markowitz, or watch his presentation in the Youtube box below: