Young Lucius wears glasses throughout the film but these were not invented until the Middle Ages. However, the film is not set in any specific time period. There are indications of an ancient Roman setting, but also of an Elizabethan setting. This was purposely done by the filmmakers, so Lucius wearing glasses is not necessarily an anachronism.
When Titus cuts Alarbus' chest, blood can clearly be seen squirting out of the knife before it has made contact with Alarbus' skin.