After winning the toss, the visitors’ innings owed much to Roderick and Hamish Marshall, the pair scoring just over half of their side’s runs. Roderick was unbeaten on 88, with Marshall departing earlier for his 51.
Gloucestershire were bowled out for 262, with Essex reaching the close on 39 for one and eyeing a substantial first-innings lead on a benign pitch.
Skipper Roderick combined watchful defence with some pleasant driving, after Australian fast bowler Matt Dixon had marked his Essex Championship debut by whipping out Cameron Bancroft and Chris Dent in his first half dozen overs.
In all, Roderick faced 172 deliveries and struck 11 fours and a six, but it was Marshall who was the most fluent. His 51 came from 60 deliveries, nine of which he struck to the boundary and all his runs came during a fourth-wicket partnership worth 73 runs.
Marshall’s fine effort was eventually brought to an end by a superb diving catch by Jesse Ryder at backward point to provide pace man Jamie Porter with one of his four wickets at a cost of 59.
Graham Napier shared the bowling honours with Porter with the evergreen Essex all-rounder picking up 3-57, those successes coming in a devastating spell of six balls that cost just a single. As a result, Gloucestershire lost their last four wickets in the space of five overs for just 23 runs.
Among Napier’s victims was Jack Taylor who scored a resolute 39, an effort containing five fours. A feature of the home side’s display was their work in the field.
Apart from Ryder’s fine effort, Alastair Cook, who caught Ian Cockbain, and Dan Lawrence also picked up fine catches, the latter reacting quickly after Tom Westley had knocked the ball up when Kieran Noema-Barnett edged a Ryder delivery.
When they replied, Essex soon lost Nick Browne, an lbw off Liam Norwell with just two runs on the board.
But Cook was confirming his authority with two fours in an over from Josh Shaw as he reached the close on 17.
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Keeping him company was Westley, who also looked assured as he collected four boundaries in his 19 to leave Essex seemingly in pole position.
Gloucestershire head coach Richard Dawson reflected: “We did some very good stuff, we would obviously have liked some more runs with the bat.
“Gareth Roderick and Hamish Marshall batted well very for us. Essex took some fine catches and we had a good spell with the ball at the end and might have picked up a couple more.”
Essex Head coach Chris Silverwood said: “I was satisfied with our bowling unit today, I thought we contained them well and it was good to see the wickets shared around.
“We’ve got a lot of hard work to do tomorrow with the bat but overall, it’s been a satisfactory day.”