The second episode of the series, in which a team of archaeologists solve mysteries from the past that cause problems in the present, pulled in 5.2m viewers and a 24.3% share of the audience at 9pm-10pm.
The series, which was developed by the team behind 'Life on Mars', debuted with 6.8m viewers and a 30.4% share of the audience last week.
A repeat of 'Doc Martin' brought ITV1 3.3m viewers and a 15.1% share of the audience in the same slot.
Channel 4's 'Gordon Ramsay's F Word', which starred actors Jessica Hynes and Rob Brydon, netted a consolidated audience of 3.1m viewers and a 14.1% share, including figures from Channel 4+1, between 9pm-10pm.
Channel Five's US import 'CSI: Crime Scene Investigation' captured 1.3m viewers and a 5.8% share between 9pm-10pm.
The latest instalment of Channel 4's 'Big Brother', in which Belinda and Rex were nominated for eviction on Friday, managed an audience of 3.3m viewers and a 19.3% share between 10pm-11pm including Channel 4+1 ratings.