According to SCOTTISH ORIGINS by Robert M. Gunn
(http://www.clan.com/history/features/origins/):
"The Romans came to Caledonia again in A.D. 80, Gnaeus Julius Agricola,
Governor of the Province of Brittania (and chief general), invaded
northern England and souther Scotland...With an army of 20,000 men,
Agricola reached the River Tay and proceeded to build fortifications to
keep out the northern tribesman, while his Roman fleet supplied him from
the channell...Agricola's Ninth Legion built the great fortified camp of
Pinnata Castra, near Inchtuthil on the River Tay."