Samuel started playing professionally in 1996 in Argentina for Newell's Old Boys, and a year later moved to Boca Juniors, where he played 103 matches and scored five goals in all competitions until 2000. In that year, Roma bought his contract for 40.265 billion Italian lire (about €20 million). He gained fame as one of the best defenders in the Italian league and gained a nickname to match, winning the Serie A title with Roma in 2001. His quality attracted interest from Spanish team Real Madrid.