Unattributed ancient Roman bronze coins described as “big and thick” typically refer to larger denomination bronze coins such as the As, Sestertius, or Follis from the Roman Republic and Imperial periods. These coins can vary significantly in size but commonly measure between 20 mm to 35 mm or more in diameter, with a substantial thickness and weight compared to smaller bronze denominations.

Roman bronze coins often feature the bust or profile of a Roman emperor, deity, or symbolic figure on the obverse and mythological, military, or civic imagery on the reverse. Due to centuries of burial, corrosion, and wear, many surviving examples are heavily worn and lack clear attribution or identifiable legends, which is why some are categorized as unattributed.

Such coins may have beaded borders, portraits, ship prows, legionary symbols, or Roman numerals indicating their denomination. The weight and size, along with visible iconographic elements, often help experts assign approximate attributions even when inscriptions are illegible.

Collectors value larger bronze coins for their bold presence, historical significance, and link to Rome’s extensive monetary history. Many coins in this category show natural patinas from oxidation, adding to their visual appeal and authenticity.

In summary, an unattributed big and thick ancient Roman bronze coin is likely a substantial denomination from the Roman Republic or Empire, prized for its robust size and connection to Rome’s imperial and civic legacy, though full identification requires details like diameter, weight, and imagery for precise classification.