Leyton Orient have signed Burnley's Alex Cisak and Dover's Connor Essam for undisclosed fees and handed deals to Alan Dunne and Frazer Shaw.
Both right-back Dunne, 32, and centre-back Essam, 23, have agreed two-year contracts with the League Two club.
Goalkeeper Cisak, 26, spent last season on loan with the O's and has also signed a two-year deal.
Ex-Dulwich Hamlet left-back Shaw, 20, has signed a one-year contract after a successful trial period with the O's.
Cisak spent the second half of last season on loan with the O's, making 19 appearances.
Dunne left Millwall earlier this summer, while Essam has previously had spells with Gillingham and Crawley.
Essam and Shaw have both previously worked with O's manager Ian Hendon.
Essam made his debut for Gillingham in 2012 when Hendon was on the coaching staff at Priestfield, and Shaw played under the 43-year-old in the under-21 set-up at West Ham United.
The quartet take the number of Leyton Orient's summer signings to nine following their relegation from League One last season.
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