The clustering of arachnoid villi along the sagittal sinus forms what is known as "Pacchioni granulations." These structures were first described in 1705 by Antonio Pacchioni, an Italian scientist. Pacchioni was born in Reggio Emilia, Italy, in 1665, and there he received his degree in medicine. Later he moved to Rome where he built a successful career dedicated to medical practice, research, and teaching. He became a friend of some of the leading scientists of his age: Lancisi, Malpighi, and Morgagni, among others. He devoted himself to elucidating the structure and function of dura mater, and in his studies often used the new technique of maceration of anatomical specimens in various fluids. Among Pacchioni's written works, the Dissertatio Epistolaris de Glandulis Conglobatis Durae Meningis Humanae (1705) deserves the greatest consideration as it contains the first description of arachnoid granulations. He compared dura to cardiac muscle and attributed to its "glandulae" (glands) the faculty of secreting lymph for lubrication of the sliding movements between meninges and brain during contractions. Three centuries after Pacchioni's death in Rome in 1726, the fine structure of arachnoid villi has not been fully elucidated; moreover, many questions related to mechanisms underlying cerebrospinal fluid absorption remain unanswered.